The US sanctions are targeted at Iran's oil sales and banking sector in order to force Iran to halt its nuclear and ballistic missile programmes, which President Trump believes the Rohani government has been carrying out covertly.
The US has also accused Iran of funding conflicts in Yemen, Syria and other parts in the Middle East.
"We believe that China's normal cooperation (with Iran) within international law is legal and legitimate, and this shall be respected," China's spokesman said while denouncing the sanctions.
The US had imposed sanctions against Iran on trade, metals and auto sectors in August after pulling out of the nuclear deal which also included its EU partners - France, Germany and Britain.
From today, the US sanctions will include Iran's lucrative oil sector which the Trump administration barring countries from trading with the country, however, it has exempted eight countries including Japan, South Korea and India allowing them leeway to trade with Iranian oil.
"Under the current circumstances, we hope all parties can bear in mind the larger picture and fulfil their duties and choose to stand on the right side of history," Hua said, adding that China will continue to "uphold the objective and responsible attitude to uphold the agreement".
Iranian President Hassan Rouhani had said his country has no fear of "new American threats," while adding that "Iran is not looking for weapons of mass destruction and never will be".
President Rohani said today that he would " proudly bypass sanctions" by the United States.
"We are in a situation of economic war, confronting a bullying power. I don't think that in the history of America, someone has entered the White House who is so against law and international conventions."
The US had imposed sanctions against Iran on trade, metals and auto sectors in August after pulling out of the nuclear deal