The British Ministry of Defense said on Friday that the UK pilots had been working with a long-standing "embed program" under which British personnel "act under the command of host nations."

It added that fewer than 10 pilots had been involved in the airstrikes.

A spokeswoman for Prime Minister David Cameron said he was aware of the pilots' role in Syria.

The disclosure came in response to a freedom of information request from a human rights group, Reprieve.

Long-standing program

The announcement has caused anger among some British politicians, who accuse the government of going back on promises that it would seek a parliamentary mandate before taking any military action in Syria.

In 2013, lawmakers voted against a motion from the prime minister authorizing military action against the forces of Syrian President Bashar al-Assad, though parliament last year approved airstrikes against "IS" militants in Iraq. The opposition Labour Party has indicated it would now support Cameron in a new vote on military action in Syria as well, but that vote has not yet taken place.

Justifying the involvement of British pilots in airstrikes in Syria without a parliamentary mandate, the ministry said they were "effectively operating as foreign troops" under the embed program, which has seen British personnel fighting under the command of foreign allies since the 1950s.

Cameron's spokewoman also told reporters that the pilots are "not operating in British jets, they are not using British weapons and they are not operating under British operations."

'Insensitivity to parliament's will'

This has failed to convince some lawmakers, with one politician from Cameron's own Conservative Party saying the government was arguing equivocally.

"There is an element of sophistry going on here ... at the very minimum, an insensitivity to parliament's will," John Baron told BBC radio.

Liberal Democrat leader Tim Farron said the participation of UK pilots in the airstrikes was "a breach of trust with the British people."

Debate in Britain about military action abroad is still colored by events in 2003, when parliament voted in favor of involvement in the US-led invasion of Iraq amid government assertions that Iraq possessed weapons of mass destruction - a justification that later turned out to be wrong.

US-led airstrikes have been conducted against "IS" in Syria since September last year after a similar air campaign was started in Iraq the month before.

tj/kms (dpa, Reuters, AFP)