Britain and France have agreed that a full range of options should be on the table in response to reports of a poison gas attack in the Syrian town of Douma which killed dozens of people on Saturday, London's Foreign Office said.
British Foreign Secretary Boris Johnson spoke to his French counterpart Jean-Yves Le Drian earlier on Monday, ahead of an emergency session of the United Nations.
"The Foreign Secretary underlined the urgent need to investigate what had happened in Douma and to ensure a strong and robust international response," the Foreign Office said in a statement.
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"They agreed that today's meeting of the United Nations Security Council in New York would be an important next step in determining the international response and that a full range of options should be on the table."
Theresa May’s spokesman added that the U.K. and its allies are working on a rapid and unified response.
French President Emmanuel Macron said in February this year that “France will strike” if chemical weapons are used against civilians in the Syrian conflict in violation of international treaties, but that he had not yet seen proof this was the case.
Macron said last May that the use of chemical weapons would represent a “red line”. In a telephone call with Russian President Vladimir Putin on Friday expressed concern over signs that chlorine bombs had been used against civilians in Syria.
Syria and its main ally Russia blamed Israel for carrying out an attack on a Syrian air base near Homs on Monday which followed reports of a poison gas attack by President Bashar al-Assad's forces on a rebel-held town.
Israel, which has struck Syrian army locations many times in the course of its neighbour's seven-year-old civil war, has not confirmed nor denied mounting the raid.
But Israeli officials said the Tiyas, or T-4, air base was being used by troops from Iran and that Israel would not accept such a presence in Syria by its arch foe.
Germany condemns Assad and Putin
Germany on Monday condemned the suspected use of chemical weapons in a opposition-held town outside Damascus, saying the circumstances pointed to Syrian President Bashar al-Assad's government being responsible for the attack.
The German government also urged Russia to "give up its blockade mentality at the U.N. Security Council" and facilitate an investigation into the use of chemical weapons in Syria. The Syrian government denied using any such weapons.
"Those responsible for the use of poison gas ... must be held to account," German government spokesman Steffen Seibert told a news conference.
"With this use of poison gas, the circumstances point to the Assad regime's responsibility," he added. "The regime's actions are abhorrent."
Germany also criticised Russia, which entered the war on Assad's side in 2015 and has blocked a number of motions related to Syria in the U.N. Security Council.
"Russia must give up its blockade mentality in the U.N. Security Council with regard to an investigation into the use of chemical weapons in Syria," Seibert said. "It must contribute constructively to a clarification."
"The Syrian regime would, without Russian and also Iranian support, not be able to keep up its approach of a ruthless, purely military solution to the conflict," Seibert added.