It is the first time the United States has applied the designation to part of a foreign government
The Syrian government condemned as irresponsible a US decision on Monday to designate Iran's Revolutionary Guards a "terrorist group", calling it a "badge of honour" for the Islamic republic.
A foreign ministry source told state news agency SANA the US move against the Islamic Revolutionary Guard Corps (IRGC) was "a blatant attack" on the sovereignty of Iran, a strong ally of Syria.
But the source said the "irresponsible step" was also recognition of the Guards' important role in defending the country's sovereignty, its independence and its resistance against the US and Israel, SANA said.
"The US move is a badge of honour," SANA said, citing the foreign ministry source.
Iran has been steadfast supporter the Syrian government during the country's civil war and a key player along with Russia and Turkey in efforts to bring the devastating conflict to an end.
US President Donald Trump said the "unprecedented" move "recognises the reality that Iran is not only a State Sponsor of Terrorism, but that the IRGC actively participates in, finances, and promotes terrorism as a tool of statecraft."
"The IRGC is the Iranian government's primary means of directing and implementing its global terrorist campaign," Trump said in a statement.
It is the first time the United States has applied the designation to part of a foreign government, rather than guerrilla groups or other informal entities.