Two British nationals and the child of a British national were among the 85 people so-far confirmed killed in the Kabul airport attack, Foreign Secretary Dominic Raab said Friday.

"I was deeply saddened to learn that two British nationals and the child of another British national were killed by yesterday's terror attack, with two more injured," Raab said in a statement.

"These were innocent people and it is a tragedy that as they sought to bring their loved ones to safety in the UK they were murdered by cowardly terrorists."

The suicide attack on a crowd trying to flee Taliban-controlled Afghanistan killed scores of Afghans including 13 US servicemen.

The blast on Thursday, claimed by the Islamic State group, targeted US forces, but hit hardest the mass of people fearing life under the Taliban who converged on the airport in a desperate bid to flee.

"Yesterday's despicable attack underlines the dangers facing those in Afghanistan and reinforces why we are doing all we can to get people out. We are offering consular support to their families," Raab said.