The discovery of three American soldiers among the dead in a suicide bombing at the opening of a girls’ school in the northwestern Pakistan town of Dir last week reignited the fears of many Pakistanis that Washington was set on invading their country.

Barack Obama has banned the Bush-era term “war on terror” and dithered about sending extra troops to Afghanistan, but across the border in Pakistan, the US president has dramatically stepped up the covert war against Islamic extremists.

US airstrikes in Pakistan, launched from unmanned drones, are now averaging three a week, triple the number last year. “We’re quietly seeing a geographical shift,” an intelligence officer said.

For the past month drones have pounded the tribal region of North Waziristan in apparent retaliation for the murder of seven CIA officers in Afghanistan by a Jordanian suicide bomber working with the Pakistani Taliban.

Last week America launched its first multiple drone attack, according to Pakistani security officials. Eighteen missiles were fired from eight unmanned aircraft in Dattakhel village, killing 16 people.

The discovery of the dead US soldiers revealed that America’s shadowy war in Pakistan not only involves drones but also small cadres of special operations soldiers.