The United States has ordered a partial evacuation of its embassy in Syria because of what it calls the uncertainty and volatility in the country.
The State Department says some non-essential embassy staff and all dependents will be leaving.
The BBC reports that in its travel advisory the State Department is also urging all American citizens to leave the country while commercial transport is still available.
The advice follows news that Washington is considering a range of targeted sanctions against the Syrian government, in response to an intensifying crackdown on popular protests by the army.
The White House said on Monday that the "brutal violence" Syria had directed against protesters was "deplorable".
US officials say sanctions could include a freeze on Syrian assets and a ban on business.
The BBC reports the remarks represent a further hardening of the US position on the Syrian protests. On Friday President Barack Obama issued a strong condemnation of the use of force.
Syrian tanks and troops advanced into the city of Deraa on Monday.
The independent Sawasiah rights organisation says it has received reports that at least 20 people have been killed in Deraa since the tanks moved in.
Sawasiah also says security forces have arrested about 500 pro-democracy sympathisers across the country.
But communications with the southern town - where the first protests against President Bashar al-Assad began on 18 March - have been cut, making it hard to confirm the information.
Rights campaigners say government forces also stormed the Damascus suburbs of Douma and Mouadhamiya, shooting and making arrests.