Iran on Thursday condemned new U.S. sanctions which punish any company that works with Syria's President Bashar al-Assad, saying they were "cruel" and would exacerbate suffering in the war-torn country.

The Caesar Act came into force on Wednesday, with the first batch of designations targeting 39 people or entities, including Assad and his wife Asma.

Iran "does not respect such cruel and unilateral sanctions waged as bullying and considers them to be economic terrorism against the people of Syria," said foreign ministry spokesman Abbas Mousavi.

The sanctions were "against international laws and human values" and would only "exacerbate the suffering of Syria's people" amid the coronavirus outbreak, he said in a statement.

Mousavi vowed that Tehran would maintain its economic ties with Damascus.

The United States imposed sanctions on Wednesday aimed at cutting off revenue for the Assad government in a bid to push it back into United Nations-led negotiations and broker an end to the country's nearly decade-long war.

Tehran has also been under U.S. sanctions since 2018, when Washington unilaterally withdrew from a landmark nuclear agreement and reimposed them, targeting the crucial oil and banking sectors.

Along with Moscow, Tehran is one of Damascus's main allies in the war that has ravaged Syria since 2011.

Russia's U.N. Ambassador Vassily Nebenzia said the United States had confirmed that "the purpose of these measures is to overthrow the legitimate authorities of Syria."

The conflict has killed more than 380,000 people and displaced millions.

(With input from AFP)