US official sources say the United States is definitely planning a military intervention in Syria and it is only a matter of time.

“The intervention will happen. It is not a question of ‘if’ but ‘when’,” the Israeli website DEBKAfile, which is believed to have close links to Israeli intelligence agencies, quoted one of the unnamed sources as saying on Saturday.

The report said a delegation from the Syrian anti-government militants is currently in Washington to talk about their requests for heavy weapons from the US government.

In their meetings with US Ambassador to Syria Robert Ford and State Department Syria expert Fred Hof, the group’s leaders handed in two lists for approval: types of heavy weapons capable of confronting Syrian President Bashar al-Assad’s armed forces and selected targets of attack to destabilize the Syrian government.

The sources added that most of the weapons have been purchased by Saudi Arabia and Qatar and are ready for shipment.

Earlier in the day, the head of the UN observer mission in Syria, Major General Robert Mood, issued a statement saying that the monitoring team was “suspending its activities” in the country due to an “intensification of armed violence,” adding, “There has been an intensification of armed violence across Syria over the past 10 days.”

UN-Arab League envoy Kofi Annan’s six-point peace plan, effective from mid-April, called for the establishment of a cease-fire between the government and the opposition and also said humanitarian groups should be allowed to have access to the population, detainees should be released, and a political dialogue should be started.

The unrest in Syria began in March 2011, with demonstrations being held both against and in support of President Assad's government.

The West and the Syrian opposition accuse the government of killing protesters, but Damascus blames “outlaws, saboteurs, and armed terrorist groups” for the unrest, insisting that it is being orchestrated from abroad.