In the past, Karzai has complained that Pakistani security forces have turned a blind eye to the Taliban's cross-border attacks, allowing them to strike and then flee back to safe havens in Pakistani territory.
But on June 15, Karzai raised his criticism to a new level. He accused Pakistani forces of supporting Taliban leaders in the tribal regions, and threatened to send Afghan troops across the border to kill extremist leaders.
"Afghanistan has the right of self-defense," Karzai said. "When they cross the territory from Pakistan to come and kill Afghans and to kill coalition troops, it exactly gives us the right to go back and do the same."
Karzai stressed that he was not threatening to invade Pakistan, saying instead that limited incursions were needed to kill specific Taliban leaders. Nevertheless, the threat angered Pakistan's new government, which summoned the Afghan ambassador to issue a formal complaint.
But U.S. President George W. Bush, asked on June 16 whether he supported Karzai's threat, made no reference to Islamabad's concerns about its sovereignty and territorial integrity. Instead, Bush urged Pakistan to work more closely with Afghan and U.S. forces in the fight against terrorism.
"Our strategy is to deny safe haven to extremists who would do harm to innocent people, and that's the strategy of Afghanistan," Bush said. "And it needs to be the strategy of Pakistan. It's in all of our interests to prevent those who murder innocent people to achieve political objectives to gain safe haven."
Bush’s comments come as relations between U.S. and Pakistani security forces appear to be at a new low. Last week, a U.S. air strike killed 11 Pakistani soldiers within Pakistani territory. The Pentagon says it targeted a group who had attacked U.S. soldiers in Afghanistan and then fled back to Pakistan.
U.S. military commanders in Afghanistan have complained for years about the trustworthiness of Pakistani security forces, telling RFE/RL and other international news organizations that informing Pakistan in advance about border operations against the Taliban meant risking the lives of U.S. troops.
Washington's growing distrust was highlighted last week by the release of a Pentagon-funded study by RAND Corporation. That study concludes that individuals in Pakistan's Frontier Corps and intelligence services support the Taliban by providing them with intelligence about the movements of coalition forces in Afghanistan.
Ahmed Rashid, a Pakistani journalist and prominent author who is critical of the international approach in Afghanistan, tells RFE/RL that Washington has become frustrated with Pakistan's military.
"There is a very massive breakdown between the U.S. and the Pakistani military. I think talks between these two have failed," Rashid says. "Whatever the details are of this clash [and air strike], we really don't know what happened. There are many versions. But I think the real issue was that the Americans are clearly sending a very tough message to the Pakistanis."
Backing From Washington?
Analysts agree that without U.S. military support, Afghan forces would have little chance of success in a battle within Pakistan's tribal agencies. But it's unclear if Washington is willing to provide that support. James Phillips, a research fellow at the Washington-based Heritage Foundation, believes Karzai’s threat does not have Washington’s backing.
"There is growing impatience in Washington with the new Pakistani government's cautious negotiations with radicals -- with the militants. But I don't see President Karzai's statement as indicating that there is backing in Washington for such a cross-border incursion," Phillips says. "President Karzai has his eye more on Afghan domestic politics. He knows that many Afghans see the Taliban as the cat's paw of Pakistan -- specifically of Pakistani intelligence. So it's popular [for Karzai] to threaten retaliation for the cross-border raids" by the Taliban, but that does not necessarily indicates that there is U.S. support for Karzai's threat, Phillips said.
Since he made the statement, Karzai has garnered considerable support among Afghans who blame Pakistan's policies for instability within Afghanistan.
There have been rallies in support of Karzai in the southeastern provinces of Paktia and Paktika as well as the western province of Herat. In the southern insurgency-plagued province of Helmand, and the northern province of Baghlan, similar gatherings have expressed support for the president.
Atta Mohammad Nur, the governor of the northern province of Balkh, said that he supports Karzai's incursion threat and that Afghans from the north are prepared to "make sacrifices" to protect the sovereignty of Afghanistan.
In Kabul, analyst Rashid Waziri tells RFE/RL that Pakistani interference in Afghan affairs is equivalent to a declaration of war. Waziri says a massive escape by Taliban prisoners on June 13 in Kandahar forced Karzai to issue a forceful warning.
"We have the right to strike our enemies inside Pakistan or its tribal territories," Waziri says. "The Turkish government gave itself the right to bomb and target Kurdish rebels in northern Iraq and to eliminate their bases. So this is an international right. And everybody can benefit from it."
But in Pakistan, such reactions are treated with suspicion. Mehmood Shah, a retired Pakistani brigadier general who formerly headed security affairs in the tribal regions, tells RFE/RL from Peshawar that Karzai's threat is provocative and violates international law.
Shah also argues that Karzai's statements, and the reactions from the Bush administration, could indicate U.S. plans to expand operations into Pakistan's tribal areas.
Shah warns that cross-border attacks by Afghan troops would undermine the global war against terrorism, and spread instability throughout the region. He also maintains that the current democratically elected coalition government in Pakistan may be too weak to formulate a comprehensive policy toward Afghanistan.
"In Pakistan, the government needs a comprehensive [anti-terror] strategy," Shah says. "This strategy needs to aim at establishing the government's authority over the tribal territories. This policy should be debated in the parliament and the Pakistani military. The ISI [intelligence service] and civilian administration need to implement such a policy wholeheartedly."
Zahid Khan is a spokesman in Peshawar for the secular Pashtun nationalist Awami National Party, which leads the provincial government in the Northwest Frontier Province. He says that as long as there are elements in Pakistan threatening and endangering the security of neighbors, Islamabad should be ready to face retaliation.
Khan maintains that the two peace deals the provincial government concluded with pro-Taliban militants in the Swat region have been effective. But he says the provincial government has been denied any role in the more significant peace deals the military was negotiating with Taliban leader Baitullah Mahsud and other Taliban commanders across the Federally Administered Tribal Areas.
"As long as there is no peace in Afghanistan, there will be no peace in [Pakistan’s] tribal areas," Khan says. In turn, if there is no peace in the tribal areas, instability throughout Pakistan and the region will follow, he says.
Khan adds that it was necessary for all sides to negotiate a peaceful settlement, and called on the Taliban to renounce violence and participate peacefully in politics. After a negotiated political settlement, "everybody should have the freedom to campaign for their ideology and ask for people’s votes. But using violence for strong-arming a country into accepting a political solution is wrong. This will only result in more innocent bloodshed," Khan says.
Bush has said the United States can help calm tensions between Islamabad and Kabul by developing a common strategy to eliminate safe havens for militants in the tribal regions -- and by working together to prevent Taliban fighters from moving freely across the border.
Bush also has suggested restarting talks between Afghan and Pakistani tribal leaders on both sides of the border. He said those talks should be conducted under the auspices of a cross-border Jirga -- a council of tribal elders -- similar to one that brought together Pashtun tribal leaders from both sides of the border in 2006. Pakistani Taliban leaders were not part of those talks.
But while such statements belie a desire for a political solution, the situation on the ground is likely to determine any future course of action. Admiral Mike Mullen, the top U.S. military commander, for now has ruled out U.S. military action in the tribal areas. Nevertheless, Mullen underscored the threat in Pakistan’s tribal areas in an interview with the “Los Angeles Times” on June 11, saying any future terrorist attack on U.S. soil is likely to originate there.