Rashid Rauf had been arrested in Pakistan but escaped custody
British Foreign Secretary David Miliband says he has asked Pakistan to clarify whether the suspected British militant Rashid Rauf is dead.
Pakistani officials said Mr Rauf was killed in a US missile attack near the Afghan border at the weekend, but this has not been independently confirmed.
Mr Rauf was accused of involvement in an alleged plot to blow up transatlantic airliners.
Mr Miliband has been visiting Islamabad as part of a regional trip.
He was answering a question about Rashid Rauf, who was believed to be on the run in Pakistan, during an exchange with students in the Pakistani capital.
Mr Miliband said Mr Rauf's family had asked the government to find out from the Pakistani authorities whether or not he had been killed in the suspected US strike.
Mr Miliband said Britain was waiting for a response.
He said without such clarification he would not comment on concerns raised by some UK lawmakers, including whether British intelligence services were complicit in what may amount to the extra-judicial killing of a British citizen.
News of the alleged liquid bomb plot paralysed global air travel in August 2006, prompting authorities to implement stringent security measures at airports around the world.
Mr Rauf was arrested in Pakistan on 9 August 2006 at the request of US authorities.
Mr Miliband said Pakistan's government had shown "reforming zeal"
Terrorism charges were eventually dropped but he remained under detention in Pakistan as a "preventative measure".
British police were seeking Mr Rauf's extradition as a suspect in the murder of his uncle six years ago.
Thought to be in his 20s and have Pakistani citizenship through family connections, Mr Rauf escaped custody in December 2007 while on his way to an extradition hearing under police guard.
Some 20 US air strikes have targeted suspected militants in Pakistan's border region in recent months.
Separately, Mr Miliband praised Pakistan for its increased dialogue with neighbours Afghanistan and India.
He said the "reforming zeal and instinct of the government is coming to the fore in a positive way and gaining the confidence of the international community".
Pakistan's government has stepped up its military operation against Taleban and al-Qaeda fighters along the Afghan border area since its election early this year.
Western powers had expressed concern the area was a "safe haven" for militants launching attacks into Afghanistan.