Foreign Secretary William Hague took the action to expel Syria’s most senior diplomat in the UK as a report by United Nations officials revealed the full horror of the atrocity.
The chargé and two other diplomats have been told to leave the embassy as the government attempted to send a tough message to Bashar al-Assad and his regime.
France, Germany, Italy, Spain, the United States, Canada, the Netherlands, Bulgaria and Australia took similar action, telling Syria’s envoys to leave their capitals in a co-ordinated move that underlined President Assad’s diplomatic isolation.
In a statement explaining the expulsions of diplomats from the US, the state department described the massacre as a “vicious assault involving tanks and artillery – weapons that only the regime possesses”.
The report by the UN said most of the dead were killed execution-style, with fewer than 20 people killed by regime shelling.
The UN reported survivors and witnesses blaming the house-to-house killings on pro-government thugs known as shabiha, who often operate as hired muscle for the regime.
Yesterday, Mr Hague renewed his calls for President Assad to adopt the six-point peace plan drawn up earlier this year by the UN-Arab League envoy, Kofi Annan, who yesterday travelled to Damascus for talks with the Syrian leader.
Mr Hague said: “We have been seeking in recent days to increase the pressure on the Assad regime and to get the message across to them that the world, the international community, is appalled by the violence that has continued, by the behaviour of the regime and by the murder of so many innocent people, including in the terrible massacre at El Houla.
“We want to get the message across to them that they have to choose, that time will run out for the Annan plan and that they have to make the choice about what they are going to do.
“So, as part of that pressure, today we have again called the Syrian chargé in London here to the Foreign Office. He has been given seven days to leave the country. Two other Syrian diplomats will be expelled at the same time, and our allies and partners around the world will be taking similar action.”
The Syrian regime has denied taking part in the massacre, instead saying the killings were the work of armed terrorists.
According to state-run news agency Sana, President Assad blamed terrorists and weapons smugglers for scuttling the peace plan.
Deputy foreign minister Faisal Mekdad said: “It is irrational that any party who wants to make Annan’s mission a success would ever commit such a massacre.”
Mr Annan called the massacre “an appalling moment with profound consequences”.
He said the regime had to take “bold steps” to show it was serious about peace.
He added that his “message of peace was not only for the government, but for everyone with a gun”.
Syria’s ally, Russia, continued to offer qualified support to the Assad regime, though it has been critical of events in Houla. Syria has seen unrest for more than a year after protests began in March 2011.