Britain's Prime Minister David Cameron said Monday that two British citizens fighting with the Islamic State group were killed by a drone strike carried out by the Royal Air Force in Syria last month. Reyaad Khan was killed after being targeted Aug. 21, when he died alongside Ruhul Amin in a drone strike in the city of Raqqa, Cameron said in an address to the members of parliament, according to BBC News.

Khan, a 21-year-old fighter with the militant group formerly known as either ISIL or ISIS, was from Cardiff, England, while Amin was from Aberdeen, Scotland. Because Khan had been planning "barbaric" attacks on the U.K., Cameron called the drone strike targeting him "an act of self-defense." Khan was killed while traveling in a vehicle, the prime minister said. A third member of the Islamic State group also was apparently killed in the strike.

"There was a terrorist directing murder on our streets and no other means to stop them," the Associated Press quoted Cameron as saying. The prime minister said the country's attorney general had approved the drone strike and that it was only "feasible" way of dealing with the danger in the situation. He also said the strike had been carefully planned and that the decision to conduct it was not taken lightly.

Cameron said the action was lawful and necessary despite the fact members of parliament previously has ruled out military action in Syria. Parliament blocked possible U.K. military action in Syria two years ago, but approved airstrikes on Islamic State group targets in Iraq in September of last year.

"I am not prepared to stand here in the aftermath of a terrorist attack on our streets and have to explain to the House [of Commons] why I did not take the chance to prevent it when I could have done," AP quoted Cameron as saying.

Another British national, Junaid Hussain, was killed by an Aug. 24 airstrike carried out by U.S. forces in a separate operation in Syria, Cameron said.