Syria has condemned Israel after air strikes against Damascus, saying the attacks aim "to give direct military support to terrorist groups" fighting the government.
Syria's Foreign Ministry a letter has been sent to the United Nations about "Israeli aggression" that killed and wounded several people and "caused widespread destruction".
Syria's government refers to rebels trying to topple President Bashar al-Assad's regime as "terrorists".
The reported Israeli air strikes hit areas in and around the Syrian capital believed to be targeting a shipment of highly accurate, Iranian-made guided missiles believed to be bound for Lebanon's Hezbollah militant group.
A senior Israeli official, who spoke on condition of anonymity to the Associated Press, confirmed Israel had launched an air strike in Damascus, but did not give any more details.
Israel has not officially confirmed or denied the attacks.
Foreign Secretary William Hague said Britain must respect Israel's actions to protect its national security and should maintain diplomatic efforts to resolve the Syria crisis.
Speaking on Sky News' Murnaghan programme, Hague said the UK needs to keep increasing the assistance its gives to the Syrian opposition "because it is only when they're in a stronger situation that the Assad regime will seriously negotiate an end to this crisis."
UN Secretary-General Ban Ki-moon urged all sides to exercise "maximum calm and restraint".