At least 12 suspected fighters were killed by two missiles fired by a suspected US drone near Wana.

That raid followed an attack in neighbouring North Waziristan, where two missiles killed 20 suspected Arab fighters, including al-Qaeda's propaganda chief, security officials said.

Sovereignty 'violated'

US forces or intelligence agents are suspected of carrying out at least 17 missile attacks in Pakistan since August. Pakistan has condemned them as violations of the country's sovereignty, but the raids have continued.

Asif Ali Zardari, the Pakistani president, warned Petraeus on Monday that the missile attacks were "counterproductive" and "detrimental to the war on terror".

"Continuing drone attacks on our territory, which result in loss of precious lives and property, are counterproductive and difficult  to explain by a democratically-elected government," the state-run Associated Press of Pakistan quoted Zadari as saying.

"It is creating a credibility gap."

However, Zardari told the Talk to Al Jazeera television programme that some of the US drone attacks on his country's soil could be "excused" as the mountainous Afghan-Pakistani border was often difficult to discern.

"If a drone comes in and targets a particular place, even the map doesn't [always] know if it's in Afghanistan or Pakistan," he said.

Zardari defended his country's co-operation with US forces operating in the region.

"There is a UN resolution on Afghanistan and, on any side of the border, there needs to be interaction so we interact with the Americans."

Petraeus's trip signals Pakistan's crucial role in Washington's so-called "war on terror", particularly in the escalating conflict in neighbouring Afghanistan.

Military operation

Pakistan has deployed security forces throughout the northwest of the country in an attempt to combat fighters sympathetic to the Taliban and al-Qaeda, which Washington says are crossing the porous border to attack US and Nato-led troops.

Petraeus is accompanied by Richard Boucher, the US assistant secretary of state, on the visit.

"They are here for previously scheduled meetings with government and military officials," Lou Fintor, US embassy spokesman, said.

Petraeus held talks with General Ashfaq Kayani, Pakistan's army chief, and Chaudhry Ahmed Mukhta, the defence minister on Monday.

Another topic that could come up during Petraeus' visit is negotiations with the Taliban. Pakistani and Afghan leaders recently vowed to seek talks with elements of the movement in an attempt to stem the surging violence.

Petraeus, previously the senior US commander in Baghdad, has indicated support for efforts to reach out to members of the Taliban considered moderate enough to co-operate with the Afghan government.