The Foreign Secretary William Hague has confirmed that the Syrian charge d'affaires and two other diplomats are to be expelled from the UK as part of a coordinated move with other countries.
He said: "Our allies and partners around the world will be taking similar action ... including France, Germany, Italy, Spain, the United States, Canada and Australia".
Canada will immediately expel the three remaining Syrian diplomats in Ottawa in response to a massacre in the town of Houla last week, Foreign Minister John Baird said.
Baird told Ottawa's CFRA radio that the trio - a charge d'affaires and two other officials - had been told they were being kicked out.
"We want to say unequivocally that this is completely unacceptable ... and we want to condemn these actions," he said, referring to the Houla killings in which more than 100 people died.
Germany is expelling Syria's ambassador following a massacre in the town of Houla last week in which at least 108 people died, a government source told Reuters.
"The move was agreed in coordination with the United States, France, Britain and other partners," said the source, requesting anonymity.
An official announcement is expected later today.
The Foreign Office is expected to announce shortly that the Syrian charge d'affaires and two other diplomats are to be expelled from the UK.
Two other diplomats are also being told to leave but the embassy in London is not being closed.
It follows the killing of at least 108 people including women and children in the Syrian town on Houla on Friday. The UN has said it is "clear" that Syrian forces were involved in shelling the town.
France's newly-elected president Francois Hollande has said that the Syrian ambassador to France will be expelled today or tomorrow, according to the news agency AFP.
The Australian Foreign Minister Bob Carr has announced the expulsion of two Syrian diplomats in protest at the killing of at least 108 civilians in the Syrian town of Houla.
He said it was currently the only way to send a "message of revulsion" to the Syrian government and that he expects other countries to do the same in the coming hours.