Anti-Israel slogans were seen on banners in Damascus, following US air strikes on a Syrian air base last week.
In the capital Damascus, dozens of Syrian students gathered outside the offices of the United Nations to protest against the US missile attack.
They held banners and chanted anti-American slogans on Saturday, such as “death to America” and “death to Israel”.
Downing Street was swift to offer its backing for the US action, which was also supported by Israel, Australia, France, Germany and European Council president Donald Tusk.
Turkey has said the US missile attack on a Syrian air base is a “cosmetic intervention” unless it removes President Bashar Assad from power.
The Syrian leader’s strong ally Iran has called for an international fact-finding committee to investigate the chemical weapons attack in a northern town that killed scores of people and trigged the American action.
Iran has been one of Assad’s strongest backers since the crisis began six years ago, leaving 400,000 people dead, half the country’s population displaced and more than five million as refugees.
It came as planes struck Khan Sheikhoun, where the chemical attack killed 87 people earlier this week.
The air raid killed a woman and wounded her son, according to the Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees.
State television reported Iranian president Hassan Rouhani insisted that the committee must be impartial and “must not be headed by Americans”.