Two separate US drone attacks on Sunday killed at least eight militants in Pakistan's lawless tribal belt known as a headquarters of Al-Qaeda, officials said.

The first attack hit a compound in Shaktoi area in South Waziristan, followed hours later by another in neighbouring North Waziristan, killing four militants on each occasion.

The compound hit in the second strike belonged to allies of the Haqqani network, which is involved in attacks on US and Afghan forces just across the border in Afghanistan, a security official said, requesting anonymity.

"They have intensified the attacks after a brief lull," Rahimullah Yusufzai, an expert on tribal affairs, told AFP of the US drone attacks after another on Saturday killed at least 12 militants in South Waziristan.

"I think they are getting intelligence, that is why the drones have become active," he said, adding that cooperation had increased recently between Pakistani and US intelligence services.

In the first strike on Sunday a US drone fired two missiles into a militant compound, a Pakistani security official, speaking on condition of anonymity, told AFP.

"We have reports that four militants have died," he said.

"One missile landed in the compound and another hit a vehicle soon after it entered the premises," he said, adding that five other militants were wounded.

It was not clear if any foreign militants were there, he said.

Waziristan has come under renewed scrutiny after Faisal Shahzad, the Pakistani-American charged over an attempted bombing in New York on May 1, allegedly told US interrogators he received bomb training there.

The United States has been increasing pressure on Pakistan to crack down on Islamist havens along the Afghan border.

Pakistani commanders have not ruled out an offensive in North Waziristan, but argue that gains in South Waziristan and the northwestern district of Swat need to be consolidated to prevent their troops from being over-stretched.

A local administration official said Shaktoi -- scene of Sunday's first strike -- was the ancestral town of former chief of Pakistan's Taliban movement (TTP) Baitullah Mehsud, who was killed in a US drone strike in August last year.

On June 1, Al-Qaeda said its number three leader and Osama bin Laden's one-time treasurer Mustafa Abu al-Yazid was killed in what security officials said was an apparent drone strike in North Waziristan.

Washington has branded the rugged tribal area on the Afghan border a global headquarters of Al-Qaeda and the most dangerous place on Earth.

Nearly 1,000 people have been killed in more than 100 drone strikes in Pakistan since August 2008, including a number of senior militants. However, the attacks fuel anti-American sentiment in the conservative Muslim country.

The US military does not, as a rule, confirm drone attacks, but its armed forces and the Central Intelligence Agency operating in Afghanistan are the only forces that deploy drones in the region.