US warns citizens to leave Syria

The State Department also said some non-essential embassy staff and all embassy dependants would be leaving.

Earlier, the US said it was considering targeted sanctions against Syria.

Meanwhile the Syrian government said in a statement troops sent to quell unrest had "restored tranquillity".

The statement, carried by the official news agency, said the government had sent troops to several cities on the request of citizens who were worried about "armed extremists".

Arrests were made and those people would be processed through the courts, it added.

On Monday witnesses said the army had advanced into the southern city of Deraa, using tanks to support troops. Security forces also reportedly opened fire in a suburb of Damascus.

There have been numerous reports of crackdowns and arrests around Syria over recent days, despite the lifting of an emergency law last week.

More than 350 people have been killed in the violence since mid-March, activists say.

The US State Department issued a warning on Monday urging all Americans to defer all travel to Syria and advising those in the country to leave while commercial transport was available.

The statement said government restrictions made it difficult to assess the security situation, adding that the authorities' attempts to blame violence on foreigners could endanger US citizens.

The Obama administration is considering sanctions to put pressure on the government of President Bashar al-Assad to stop its crackdown, US officials say.

The steps could include a freeze on the assets of Syrian leaders and a ban on business dealings in the US - but no time scale has been given for the measures.

According to a UN Security Council diplomat, the UK and other European states are circulating a draft statement condemning the violence in Syria.

Opposition activists said Monday raid on Deraa involved as many as 5,000 soldiers and seven tanks.

Tanks surrounded the Omari mosque in the old city with snipers firing from rooftops, killing 25, anonymous opposition sources said.

Deraa is the city where protesters began calling for political reforms last month. Many are now demanding that President Assad step down.