Eight Western powers have announced that they are expelling senior Syrian diplomats following the killing of 108 people in the Houla region of Syria on Friday.
France, Britain, Germany, Italy, Canada, the Netherlands and Australia have all announced expulsions. Spain followed their lead hours later, saying Madrid rejected the escalation of violence in Syria.
The Syrian "ambassador and four other (Syrian) diplomats have 72 hours to leave Spanish territory," a formal statement said.
Most victims of Friday's massacre were summarily executed, according to the UN, including 49 children and 34 women.
French President Francois Hollande told reporters Tuesday that Ambassador Lamia Shakkour will be notified "today or tomorrow" that she must leave.
British officials said three Syrian diplomats would be expelled, among them Charge d'Affaires Ghassan Dalla – Syria's top ranking diplomat in London.
Australian Foreign Minister Bob Carr said Charge d'Affaires Jawdat Ali, the most senior Syrian diplomat in Australia, is to be expelled along with another diplomat.
The move comes one week after reports in Washington indicated senior administration officials are on the verge of arming Syria's rebels - providing they can ensure any weapons provided will not fall into the hands of terrorists.
The move, which has been advocated by senior officials in Western Europe for several months, would mark a major shift in Western posture on the Syrian crisis and could herald deeper direct involvement in the fighting there.
Action from the United States against Syrian diplomats is also expected.