Image copyright AP Image caption Ground troops are being sent in after several weeks of air strikes, the army says

The Pakistani army says it has launched a ground offensive against Taliban militants in North Waziristan.

A statement said operations had begun around Miranshah, the main town in the tribal region bordering Afghanistan.

The move follows air strikes which the army says have killed 370 militants. There is no confirmation of the figure.

North Waziristan has long been a sanctuary for militants. Correspondents say many are thought to have left the area before the offensive began.

The assault comes three weeks after militants attacked Pakistan's largest airport in Karachi, leaving more than 30 people dead.

For the past two weeks, Pakistani forces have been carrying out air strikes against what it says are militant hideouts in North Waziristan.

Among their targets, they say, have been Uzbek militants who claimed responsibility for the Karachi attack and their Pakistani Taliban (TTP) allies.

Monday's army statement said troops were now conducting a door-to-door search in Miranshah.

"Troops have recovered underground tunnels and IED [improvised explosive device] preparation factories," it said.

The town has been one of the main TTP bases during recent years when militants who had at times been tolerated by the military killed thousands of people in a bombing campaign across Pakistan.

Analysis: M Ilyas Khan, BBC News, Islamabad

Pakistani troops have finally moved into the town of Miranshah in North Waziristan to clear what has long been seen as the last major sanctuary for al-Qaeda and Taliban militants in the Afghanistan-Pakistan region.

But there are still questions over whether Pakistan intends to eliminate the militants completely.

The offensive, demanded by the international community but resisted by Pakistan for several years, comes after a daring militant attack on Karachi airport earlier this month. But many believe what actually tipped the balance is Pakistan's need to secure its borders ahead of the Nato withdrawal from Afghanistan.

It's not clear what the infantry will find in Miranshah. Most militants left the town weeks ago and have fanned out to areas not only in Afghanistan and Pakistan, but also within the North Waziristani hinterland south and west of the town, where there is no looming threat of a ground offensive.

Where have all Pakistan's militants gone?

In public statements, Pakistani commanders have said they will not discriminate between so-called good and bad Taliban, reports the BBC's Andrew North in Islamabad.

But our correspondent says there are widespread reports from within North Waziristan that many militants were allowed to escape before the operations began.

Nearly half a million people have left North Waziristan since the offensive was announced following the Karachi airport attack.