DERA ISMAIL KHAN, Pakistan (Reuters) -- Pakistani helicopter gunships attacked Taliban bases near the Afghan border as the army urged NATO forces to seal the frontier to stem crossborder movement of militants.
Pakistani forces launched an offensive to wrest control of the lawless South Waziristan region on October 17 after militants rocked the country with a string of bomb and suicide attacks in recent weeks, killing more than 150 people.
Six people were killed in two suicide bomb attacks at the International Islamic University in the capital, Islamabad, on October 20, prompting authorities to order the closure of educational institutions across the country.
Remote and rugged South Waziristan, with its rocky mountains and patchy forests cut through by dry creeks and ravines, is a global hub for militants.
The offensive is being closely followed by the United States and other powers embroiled in Afghanistan.
The government forces initially faced light resistance but fighting intensified as soldiers approached the militants' main sanctuaries in the mountains.
Government forces attacked the militant strongholds of Makeen and Ladha with helicopter gunships and artillery on October 21, security officials said. Eight soldiers wounded in overnight fighting were evacuated to the nearby town of Dera Ismail Khan.
Fighting for control of the lawless area is seen a major test of the government's ability to tackle increasingly brazen insurgents who have carried out daring attacks across Pakistan, including on the army headquarters.
Qari Hussain Mehsud, a senior Taliban commander known as "the mentor of suicide bombers," called the BBC on October 20 to take responsibility for the attacks on the Islamic University and said the militants consider "all of Pakistan to now be a war zone."
The security officials said heavy exchanges of fire were taking place in Kotkai, Hussain's hometown and also the birthplace of Pakistani Taliban chief, Hakimullah Mehsud. The town is on the approach to a main base area.
Security forces briefly took control of Kotkai in fighting on October 19 but militants recaptured it in a counterattack.
Seal Afghan Border
As government forces pressed ahead with the Waziristan offensive, the military called on the NATO troops in Afghanistan to seal the border "to prevent crossborder movement and flow of weapons."
Pakistan Joint Chiefs of Staff Committee (JCSC) Chairman General Tariq Majid made the call during talks with Britain's Chief of Defense Staff, Jock Stirrup.
Pakistani newspapers have in recent days reported that NATO forces had abandoned border posts opposite South Waziristan, raising the possibility of Afghan Taliban coming to help their Pakistani comrades, or of Pakistani Taliban fleeing.
Majid called for "synchronization of effort on both sides and sharing of real-time intelligence with reference to the ongoing operations," an army statement issued late on October 20 said.
The army says 90 militants and 13 soldiers have been killed since the offensive was launched on October 17 but there was no independent confirmation of those tolls.
Foreign reporters are not allowed anywhere near the battle zone and it is dangerous for Pakistani reporters to visit. Many of the Pakistani media based in South Waziristan have left.
About 28,000 soldiers are battling an estimated 10,000 hard-core Taliban, including about 1,000 tough Uzbek fighters and some Arab Al-Qaeda members.
More than 100,000 civilians have fled from South Waziristan, with about 32,000 of them leaving since October 13, the United Nations said. Up to 200,000 people could flee, the army says.
The army has launched brief offensives in South Waziristan before, the first in 2004 when it suffered heavy casualties before striking a peace pact.