Britain's Prime Minister Theresa May during a press conference in 10 Downing Street, London. Picture: Simon Dawson/Pool Photo via AP

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

The UK debate comes as the European Union's foreign ministers joined together to say they understood the need for the airstrikes and called for a new push for a political solution to the war in Syria.

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

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

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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 plans to say, according to excerpts of her speech — linking the chemical attack in Syria with the poisoning of a former Russian spy and his daughter last month with a military-grade nerve agent in the English city of Salisbury.

Foreign Secretary Boris Johnson said Monday that the airstrikes against Syria, 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 British government said it would seek an emergency House of Commons debate on the airstrikes so legislators could have their say. Such an 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.

French Prime Minister Edouard Philippe is to deliver a speech to the National Assembly, France's lower house of parliament, on Monday afternoon. He is expected to insist on France's "legitimacy" to launch airstrikes on Syria.

French President Emmanuel Macron, left, welcomes Canadian Prime Minister Justin Trudeau at the Elysee Palace in Paris. Picture: Michel Euler/AP

The speech will be followed by a debate, but a vote on France's participation in the Syria airstrikes is not anticipated.

Under the French Constitution, the government must inform the parliament, but a vote is requested only if a military intervention is expected to last more than four months.

In Luxembourg, the foreign ministers of the 28 EU countries called for a political breakthrough involving regional players to put Syria on track to a peaceful solution of its seven-year conflict.

Britain's ambassador to the Netherlands and permanent representative to the chemical weapons watchdog OPCW, Peter Wilson, centre, talks to embassy employees after a press conference in The Hague. Picture: Michael Kooren, pool photo via AP

The ministers said the EU "understands" the need for the coordinated U.S, French and British airstrikes against Syrian regime targets following the suspected April 7 chemical attack in Douma.

They insisted it was executed with "the sole objective to prevent further use of chemical weapons and chemical substances as weapons by the Syrian regime to kill its own people."

French Foreign Minister Jean-Yves Le Drian said he welcomed the EU's unanimous backing.

EU foreign policy chief Federica Mogherini said the EU wants to use a major meeting on Syria in Brussels next week to give impetus to United Nations peace efforts following the airstrikes.

"There is the need to give a push to the U.N.-led process," Mogherini said.

More than 70 delegations are expected to attend the April 24-25 Syria donor conference in Brussels.

"We should keep on pushing for a solution through the U.N. Security Council. It's the only way forward," Dutch Foreign Minister Stef Blok said.

AP