DERA ISMAIL KHAN:More than 30,000 Pakistani soldiers launched a ground offensive against al-Qaida and the Taliban's main stronghold along the Afghan border today, officials said, in the country's toughest test yet against a strengthening insurgency.

The United States pushed the government to carry out the assault in South Waziristan, and it comes after two weeks of militant attacks that have killed more than 175 people across the nuclear-armed country. That has ramped up pressure on the army to act.

Pakistan has fought three unsuccessful campaigns since 2001 in the region, which is the nerve-centre for Pakistani insurgents fighting the US-backed government. It is also a major base for foreign militants planning attacks on American and NATO forces in Afghanistan and on targets in the West.

After months of aerial bombing, troops today moved into the region from several directions, heading to the insurgent bases of Ladha and Makeen among other targets, intelligence and military officials said on condition of anonymity because of the sensitivity of the topic or because they were not allowed to brief the media.

They said the operation was expected to last around two months.

Pakistani army spokesman Major General Athar Abbas confirmed this evening that a full-fledged ground operation was underway, and said that it aimed to "uproot" the Pakistani Taliban. He said it was too early to discuss what sort of resistance the army was meeting.

The United Nations has said it is preparing to help civilians that are fleeing the region. Up to 150,000 civilians have already left in recent months after the army made clear it was planning an assault, but there are perhaps as many as 350,000 remaining.

At least 11 suspected insurgents were killed in the jet bombings, while a bomb hit a security convoy, killing one soldier and wounding three others, two local intelligence officials said.

It is nearly impossible to independently verify information from the region, which is largely controlled by local tribes and has little infrastructure or government presence. Foreigners require permission to enter tribal areas and few Pakistani journalists from other parts risk travelling there.

Makeen resident Ajmal Khan said people there were terrified but could not leave their homes due to a curfew. "We heard sounds of planes and helicopters early this morning. Then we heard blasts," Khan said via telephone. "We are also hearing gunshots and it seems the army is exchanging fire with Taliban." The army has deployed more than 30,000 troops to the region, said one of the intelligence officials. The military already has said it has sealed off many supply and escape routes and has been trying to secure the support of local tribesmen in the fight.

Earlier this week, the airport in the nearest major town, Dera Ismail Khan, was closed to civilian aircraft.

Recent opinion polls show broad support for military action against the militants, a change from a few years ago. There is also political backing for action. But a long and bloody conflict - and more terror attacks around the country - could erode that support.

Speaking earlier in the week, army spokesman Abbas said the assault would be limited to slain Pakistani Taliban leader Baitullah Mehsud's holdings - a swath of territory that stretches roughly 1,275 square miles. That portion covers about half of South Waziristan, which itself is slightly larger than the US state of Delaware.

The plan is to capture and hold the area where Abbas estimates 10,000 insurgents are headquartered and reinforced with about 1,500 foreign fighters, most of them of Central Asian origin. "There are Arabs, but the Arabs are basically in the leadership, providing resources and expertise and in the role of trainers," he said.

Since 2001, the army's three attempts to dislodge Taliban fighters from South Waziristan have ended in truces that left the Taliban in control. This time the military has said there will be no deals, partly to avoid jeopardising gains won earlier this year when Pakistani soldiers overpowered the Taliban in the Swat Valley, another northwest region.

Taliban spokesmen could not immediately be reached for comment today. Communications in and around the region appeared jammed, making it difficult to reach local residents or other witnesses.

Despite sometimes rocky relations with the Pakistani military, the US is trying to rush in equipment for the offensive that would help with mobility, night fighting and precision bombing, a U.S.

In addition to night-vision devices, the Pakistan military has said it is seeking additional Cobra helicopter gunships, heliborne lift capability, laser-guided munitions and intelligence equipment to monitor cell and satellite telephones.