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Mr. Hollande said that after high-level discussions with British Prime Minister David Cameron and U.N. Secretary-General Ban Ki-moon, it had been decided to deploy “a certain number of … pressure tactics” against Syria, including the expulsion of the ambassador.

Germany on Tuesday announced that Syria‘s ambassador, Radwan Loutfi, had 72 hours to leave. German Foreign Minister Guido Westerwelle said his country and its allies hope “that this unambiguous message does not fall on deaf ears in Damascus.”

“The Syrian regime bears responsibility for the terrible events in Houla,” Mr. Westerwelle said in a statement. He said Germany will push for the U.N. Security Council to consider the situation in Syria again.

“It has been clear not just since Houla that Syria has no future under Assad,” Mr. Westerwelle said. “He must clear the way for peaceful change in Syria.”

The Italian Foreign Ministry said Ambassador Khaddour Hassan was summoned and informed that he must leave. Spain said it was giving Syrian Ambassador Hussam Edin Aala and four other diplomats based in Madrid three days to leave the country.

Mr. Baird said these “Syrian representatives are not welcome in our countries while their masters in Damascus continue to perpetrate their heinous and murderous acts.”

Australia gave Syrian Charge d’Affaires Jawdat Ali, the most senior Syrian diplomat in Australia, and another diplomat from the Syrian Embassy 72 hours to leave the country.

Dutch Foreign Minister Uri Rosenthal declared the Syrian ambassador to his country “persona non grata.” ”It is no longer possible to work with a country with such a president,” Mr. Rosenthal said on the ministry’s official Twitter feed.

In Vienna, Austria, Foreign Ministry spokesman Nikolaus Lutterotti said the Syrian ambassador is being summoned to the ministry, where officials will deliver a very hard protest about the massacre.

When asked if the expulsions were EU-wide, Mr. Lutterotti said this had not yet been decided. He said the ambassador to Austria would not be expelled as he holds an additional function as the representative to the U.N. organizations in Vienna.

There was no public Syrian reaction to the coordinated expulsions. Phone calls to Syria‘s embassy in Paris were not answered, and an official at the Syrian delegation to UNESCO refused to comment.

The United Nations estimates 9,000 people have been killed since the uprising began in March 2011.

Mr. Hollande said Tuesday that Paris will host a meeting in early July of the so-called Friends of Syria to seek a diplomatic solution to the conflict. The ambassador’s expulsion came amid increasing diplomatic efforts to end the bloodshed in Syria and put pressure on Mr. Assad.

The United States, Britain and France are among countries that have closed their embassies in Syria since the crackdown on protesters began last year.

Associated Press reporters across Europe, in Australia and in Canada contributed to this article.