Hillary Clinton warns of 'severe consequences' for Pakistan if a new attack like the Times Square bomb is traced back to the country

An American drone killed at least nine people in Pakistan's tribal belt this morning in the first such strike since a Pakistani-American man was linked to last weekend's failed Times Square bombing.

Two missiles slammed into a house in North Waziristan, the tribal agency where the 30-year-old bombing suspect Faisal Shahzad claims to have met the Taliban leadership and obtained explosives training.

The US has stepped up pressure on Pakistan to attack militant hideouts in the tribal belt in recent days, particularly North Waziristan. Using unusually belligerent language, the US secretary of state, Hillary Clinton, warned of "very severe consequences" if a successful attack was linked to Pakistan.

In an interview due to be broadcast on CBS on Sunday, she said the US "wants more, expects more" from Pakistan.

"We've made it very clear that if, heaven forbid, an attack like this that we can trace back to Pakistan were to have been successful, there would be very severe consequences," she said.

The US military commander in Afghanistan, General Stanley McChrystal, reportedly delivered a similar message to the Pakistani army chief, General Ashfaq Kayani, in a meeting last Friday.

Clinton's threat is understood to mean the US could slow millions of dollars in economic and military aid, rather than mount directly military action in the tribal belt, although some American politicians have raised voices in favour of that, too.

In fact, the US is already engaged in its most ferocious campaign on Pakistan soil for decades through the CIA drone strikes, which are currently averaging about two per week.

A senior Pakistani intelligence official said there had been 40 drone attacks so far this year, compared with 49 in the whole of 2009. Other tallies have counted just over 30 strikes in 2010.

The CIA has received permission to strike a much wider range of suspected militants than before, including those whose identities have not been established, the Los Angeles Times reported last week. Previously, the CIA could only attack individuals on a vetted list of Taliban and al-Qaida leaders.

Today's drone strike destroyed a compound in Datta Khel, a notorious militant stronghold close to the Afghan border. One villager told Reuters that drones circled over the destroyed compound for some time after the attack; the identity of those killed is not known.

"The Americans are very anxious and angry," said Dr Riffat Hussain, an Islamabad-based defence analyst. "Hillary is sounding a word of warning to Pakistan, and this latest drone strike may be related to that."

However, the nature of any link between the Taliban and the Times Square attack remains unclear. The crude nature of the bomb, the bungled nature of its execution and the fact that Shahzad so readily admitted his terrorist links suggest the Pakistani-American had little training.

Additional FBI investigators are due to arrive in Pakistan to determine whether Shahzad was a "lone wolf" or had been deployed by a militant network. Several associates who have been picked up for questioning in Pakistan belong to Jaish-e-Muhammad, a militant group.

Separately, a Pakistani army helicopters gunship killed 18 militants and destroyed six militant hideouts during operations in Orakzai, another corner of the tribal belt where Taliban fighters recently beheaded three men, according to a government official in the area. The toll could not be independently verified.