Prime Minister Theresa May is set to face restive British lawmakers Monday to justify her decision to launch airstrikes against Syria without a vote in Parliament.

Royal Air Force jets joined American and French warplanes and ships in hitting targets in Syria Saturday in response to a reported chemical attack in the town of Douma.

Parliament, which returned Monday after a spring break, was not consulted about the action. The government is not legally bound to seek lawmakers' approval for military strikes, though it is customary to do so.

May's office said Monday that she plans to tell lawmakers that the airstrikes were "in Britain's national interest," were carried out to stop further suffering from chemical weapons attacks and had broad international support.

"We cannot allow the use of chemical weapons to become normalized, either within Syria, on the streets of the U.K. or elsewhere," May will say — linking the chemical attack in Syria with the poisoning of a former Russian spy with a nerve agent in the English city of Salisbury.

Foreign Secretary Boris Johnson said Monday that the strikes, which targeted three chemical weapons sites, had been "calibrated and proportionate."

He said the action was "not an attempt to change the tide of the war in Syria or to have regime change."

In an unusual move, the government says it will seek an emergency House of Commons debate on the airstrikes so legislators can have their say.

That after-the-fact debate— which may not include a vote — is unlikely to satisfy angry opposition lawmakers.

Jeremy Corbyn, leader of the main opposition Labour Party, said Britain should introduce a War Powers Act to ban military action without Parliament's approval.

Corbyn said Sunday that he was not convinced the military intervention had been legal under international law.

"It looked awfully to me as though the prime minister was more interested in following Donald Trump's lead than anything else," Corbyn said.