A barrage of US missiles targeted Pakistan's Khyber district on Friday for a second consecutive day, killing 16 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 Friday destroyed a compound in the Sipah area, killing at least five militants. A drone then fired two missiles into another compound in the Malakdin Khel area, killing five militants.
Pakistani officials reported a third missile strike from an American drone in Sandana village.
"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 indicated that a compound of local group Lashkar-e-Islam was also destroyed.
The US president in Washington on Thursday unveiled a review of his strategy to defeat Al-Qaeda and reverse the nine-year Afghan Taliban insurgency.
Obama welcomed Pakistan's efforts against Islamist extremists, which in particular has seen the army beat back the Taliban from South Waziristan in the tribal belt and Swat, a northwest former tourist spot.
"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. "When we hear the Pakistani military say it's not a question of whether but when, we're encouraged.
"We would like it to be soon because we see these people as our common enemy but we understand that the decision has to be made by the leadership of the Pakistani military," 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.
Accompanied by a huge business delegation, Wen is the first Chinese premier in five years to visit the nuclear-armed country.
A mortar attack in Pakistan's northwest town of Hangu killed nine people, including women and children, in what police called a sectarian attack.