DERA ISMAIL KHAN, Pakistan (Reuters) -- Pakistan's army has begun a ground operation against Taliban militants in the South Waziristan region on the Afghan border, with soldiers advancing from three directions, officials said.
The assault, which began on October 17, follows a string of brazen militant attacks that began on October 5 with a suicide bomb attack on a U.N. office in Islamabad and included assaults on the army headquarters, police and the public in which more than 150 people were killed.
In a show of unity before the offensive, government and political party leaders gave the military full backing on October 16, vowing to weed out militants and restore the writ of the state.
"The ground operation has begun," Tariq Hayat Khan, secretary of Pakistan's ethnic Pashtun tribal regions, told Reuters by telephone.
He gave no details and military spokesmen were unavailable for comment.
Intelligence and government officials said troops were moving from three directions and some clashes had erupted when they met resistance. Four soldiers were wounded, an official said.
A military official referred to the troop movements as "pre-positioning".
The army says about 28,000 soldiers are in place to take on an estimated 10,000 hard-core Taliban. About 500 commandos arrived in the region on October 16, security officials said.
The army has for months been using aircraft and artillery to to soften up the militants' defenses while moving in troops to seal off the region.
The army has stepped up its air and artillery attacks in recent days while thousands of civilians have been fleeing.
Army chief General Ashfaq Kayani briefed government and party leaders on October 16 and they all agreed that the militants posed a serious threat to the sovereignty and integrity of the state.
"The national consensus is reaffirmed to establish and maintain the writ of the state to weed out these elements," Prime Minister Yusuf Raza Gilani's office said.
More than 80,000 civilians had fled from South Waziristan in anticipation of the offensive and the U.N. refugee agency said more people left this week.
Earlier, a government official said authorities had imposed a curfew along roads in South Waziristan to protect forces moving towards militant strongholds.
An intelligence official said soldiers, tanks and artillery were being taken towards militant areas. Telephone services had apparently been cut off to the region.
Roadside bombs went off near military convoys in both South and North Waziristan regions, killing three soldiers and wounding five, another intelligence official said.
Pakistani Taliban made advances towards Islamabad early this year, raising fears about the stability of the U.S. ally.
But significant military gains in the Swat valley, northwest of Islamabad, have reassured the United States and other allies about Pakistan's commitment to the fight.
In a sign of U.S. continuing support, President Barack Obama signed on October 14 a $7.5 billion aid bill for Pakistan over the next five years.
But Pakistan's military had complained about the bill because the legislation ties some funds to fighting militants and is seen by critics as violating sovereignty.
Foreign Minister Shah Mehmood Qureshi was in Washington this week when Democratic Senator John Kerry, an author of the bill, issued a statement stressing that the legislation did not seek to impinge on Pakistan's sovereignty or "micromanage any aspect of Pakistan's military or civilian operations".
Qureshi told parliament on October 16 the country had not compromised its sovereignty and he later met army chief Kayani.
"Many of the fears that were expressed, concerns that were shown earlier on, have been allayed by the statement," Qureshi told Dawn television, referring to Kerry's statement.