Britain is prepared to carry out more drone strikes against British jihadis in Syria plotting attacks on the United Kingdom, Defense Secretary Michael Fallon said Tuesday. Fallon added that the Royal Air Force drone strike that killed two British citizens in Raqqa, Syria, last month, which was first revealed on Monday by Prime Minister David Cameron, was entirely legal.

“There was no other way of dealing with these particular terrorists, they weren’t going to come back to this country to be prosecuted or stand trial. There was no other way of preventing the kind of armed attack they were involved in planning,” Fallon said, during an interview with ITV, cited by the Guardian.

“Any country has the right to defend itself from an armed attack and that’s what we did.”

The attack reportedly killed Reyaad Khan from Cardiff and two other Islamic State group fighters, including another Briton, Ruhul Amin.

Fallon refused to give details about the target the men were plotting to strike, but said it was a planned attack on “a major event, one of our parades.”

"We wouldn't hesitate to do it again. If we know there's an armed attack likely, if we know who's involved in it, we have to do something about it," Fallon told BBC Radio.

The men were reportedly working for the Islamic State group in Syria at the time, according to Cameron on Monday. "There was a terrorist directing murder on our streets and no other means to stop him," Cameron said. "We took this action because there was no alternative."

The airstrikes were approved by the country’s attorney general, the main legal counsel to the U.K., despite the lack of a parliamentary mandate to take military action in Syria. Cameron said the strike had been an act of self-defense. "There was clear evidence of the individuals in question planning and directing armed attacks against the UK," he said.

The strikes have been criticized by international watchdogs. Amnesty International U.K. Director Kate Allen said it was "extremely alarming that the U.K. has apparently been conducting summary executions from the air,” Al Jazeera reported.

"In following the United States down a lawless road of remote-controlled summary killings from the sky, the RAF has crossed a line," she added, referring to the recently revealed CIA-led American drone strike program in Syria.