British Prime Minister Theresa May said she would talk to President Donald Trump later on Tuesday about a suspected chemical attack in Syria, as the United States considers a multinational military response.
Trump promised forceful action on Monday in response to a suspected Syrian poison gas attack that killed at least 60 people and injured more than 1,000 others. US officials said military options were being developed.
May, wary of the domestic political risks of promising military action, has so far focused on the need to discover the facts about the attack and establish a common international response.
But, she has also said that those responsible must be held to account and British diplomats have indicated that all options remain on the table.
"I'll be continuing to talk with our allies and partners as I have done, speaking to President Macron this morning, and I'll be speaking to President Trump later today," she told reporters in Cambridgeshire in eastern England.
Britain currently conducts air strikes in Syria from its military base in Cyprus, but only against targets linked to the Islamic State group.
Parliament voted down military action against President Bashar al-Assad's government in 2013, in a major embarrassment for May's predecessor David Cameron that then deterred the US administration of Barack Obama from similar action.
When asked whether Britain would join the United States if Washington decided on further military action in Syria, May declined to answer the question directly but said: "We believe that those responsible should be held to account."
May has already faced calls from some members of her party to consider committing to a military response without asking parliament's approval. The British parliament is currently not in session, and resumes on April 16.
Although not a legal requirement, parliament has voted on taking offensive military action since a 2003 vote on the US-led invasion of Iraq. That was seen as the first step towards establishing a constitutional convention, which has been observed in subsequent military deployments in Libya and Iraq.
May said she would chair a meeting of Britain's National Security Council later on Tuesday.
"This attack that took place in Douma is a barbaric attack. Obviously we are working urgently with our allies and partners to assess what has happened on the ground," she said.