Syrian forces have fired "Scud-type missiles" at rebels in the north of the country, escalating the conflict, US and Nato officials have said.
A number of short-range, unguided ballistic missiles had been launched, the officials said.
The US state department would not confirm the type but said missiles had been deployed. It said Syria was resorting to "more vicious weapons".
Separately, a series of blasts has hit the Syrian capital Damascus.
A US official quoted by Reuters and Associated Press confirmed the use of Scud-type missiles.
AP quoted the official as saying that more than half a dozen missiles were fired from the Damascus area into northern Syria. There was no indication any chemical weapons had been used, the official said.
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