A barrage of US missiles targeted Pakistan's Khyber district on Friday for a second consecutive day, killing 25 militants as Barack Obama urged Islamabad to do more to root out terror havens.

Pakistani officials said three drone strikes destroyed targets in Khyber, the tribal district nearest to the northwestern capital of Peshawar and this week seemingly subject to an expansion of the covert American campaign.

Missiles slammed into compounds in different villages of Tirah, the same valley where a US drone attack on Thursday killed seven militants in either the first or second such strike in Khyber, local officials said.

The first strike destroyed a compound belonging to local militant group Lashkar-e-Islam in Sipah, a remote region where government security forces have no presence, and killed six militants, Pakistani intelligence agents said.

Another drone fired two missiles into another compound in the Malakdin Khel area, which the officials said killed 13 militants, raising an initial toll of five dead.

Pakistani officials later reported a drone strike in Sandana village in Khyber, which straddles NATO's main land supply line through Pakistan to its estimated 140,000 troops in Afghanistan.

"A number of missiles hit a militant compound. Six militants were killed," a security official in Peshawar told AFP.

Washington considers Pakistan's lawless tribal belt the global headquarters of Al-Qaeda and says eliminating the militant threat is vital to winning the nine-year war against the Taliban in neighbouring Afghanistan.

The United States does not confirm drone attacks, but its military and the Central Intelligence Agency operating in Afghanistan are the only forces that deploy the aircraft in the region.

The United States has this year doubled missile strikes in Pakistan's tribal belt with around 100 attacks killing more than 600 people since January 1.

Most have been concentrated in North Waziristan, the most notorious Afghan Taliban and Al-Qaeda stronghold in Pakistan, where the United States wants the Pakistan military to launch a ground offensive as soon as possible.

Intelligence officials said Khyber was being targeted because militants had recently moved into the area from Orakzai, the home district of Pakistan's Taliban chief Hakimullah Mehsud, and Afghanistan's Nangarhar province.

Intercepts suggested that the militants thought they would be relatively safe in Khyber, which has been previously shielded from US missile attacks, and where they could have sought protection from Lashkar-e-Islam.

The faction, whose name means Army of Islam, is linked to the Taliban and has attacked NATO supply convoys.

Obama on Thursday unveiled a review of his strategy to defeat Al-Qaeda and reverse the nine-year Afghan Taliban insurgency, welcoming Pakistan's assistance following a series of offensives in the last 20 months.

"Nevertheless progress has not come fast enough, so we will continue to insist to Pakistani leaders that terrorist safe havens within their borders must be dealt with," Obama said.

US ambassador to Islamabad Cameron Munter told reporters that US officials would like to see Pakistan launch an offensive in North Waziristan "tomorrow" but acknowledged that troops were stretched too thin to act immediately.

"I think it would be incorrect to define the question about North Waziristan as a question simply of will rather than of capacity," he said.

"I think there is a capacity issue."

There are around 140,000 Pakistani security forces in the northwest border region, more than the estimated 100,000 American troops in Afghanistan.

"When we hear the Pakistani military say it's not a question of whether but when, we're encouraged," Munter said.

Pakistan marked the holy day of Ashura, which has been marred in the past by bomb attacks, under blanket security as Chinese Premier Wen Jiabao arrived on a three-day visit aimed at finalising 20 billion dollars' worth of trade deals.

A mortar attack in Pakistan's northwest town of Hangu killed nine people, including women and children, in what police called a sectarian attack.

Police in the south said they shot a suicide bomber who blew himself up while trying to access a Shiite parade in Sindh province, but that he wounded only three policemen.