The withdrawal of Iranian forces is not up for discussion, the Syrian deputy foreign minister was quoted as saying on Wednesday, after Washington demanded they pull out of Syria's conflict.

U.S. Secretary of State Mike Pompeo has demanded Iran make sweeping changes — from dropping its nuclear program to leaving the Syrian war — or face severe economic sanctions.

"Whether Iranian forces or Hezbollah withdraw or stay in Syria is not up for discussion because it's the [business] of the Syrian government," Lebanon's al-Mayadeen TV cited Syrian Deputy Foreign Minister Faisal Mekdad as saying.

In Syria's seven-year conflict, Iran, along with Russia, has provided vital support to President Bashar al-Assad's military. Iran's Revolutionary Guard Corp forces and the militias it backs from the region, including Lebanon's Hezbollah, helped Damascus claw back control of major cities from militants and rebels.

Syria's neighbour, Israel, has also resented the Iranian incursion, striking at Hezbollah targets in Syria.

Pompeo said Iran must withdraw all forces under its command in Syria. Tehran dismissed the U.S. ultimatum, and one senior official said it showed the United States seeks "regime change" in Iran.

Secretary of State Mike Pompeo said the U.S. will continue sanctioning Iran if it continues to deploy forces to Syria and support Hezbollah in Lebanon. (Michael Reynolds/EPA-EFE)

Mekdad added that Damascus plans to take back every inch of the country, and the next target could be north or south after crushing insurgents in a string of enclaves around the capital.

"This is our decision and the decision of our friends," the pro-Syrian government channel cited him as saying in an interview with Russian state news agency Sputnik. "After ending the direct terrorist danger to Damascus, the door is open to heading north or south."

Europeans still support JCPOA

Pompeo's demands came in the wake of U.S. President Donald Trump announcing earlier in the month that he would pull the U.S. out of the multilateral nuclear accord with Iran that his predecessor, Barack Obama, helped spearhead.

France, one of several European powers dismayed by the U.S. withdrawal from the 2015 nuclear pact, said Wednesday that Washington's method of adding more sanctions on Tehran would reinforce the country's dominant hardliners.

"We disagree with the method because this collection of sanctions which will be set up against Iran will not enable dialogue and, on the contrary, it will reinforce the conservatives and President [Hassam] Rouhani. This posture risks endangering the region more," Jean-Yves Le Drian told France Inter radio.

Le Drian said Paris would continue to implement the agreement even if it did agree with the United States that Iran's ballistic missile activity and regional hegemonic ambitions needed to be curbed.

He said Paris shared Washington's concerns over Iran's ballistic missile "frenzy" and regional ambitions, but the 2015 nuclear deal was the best chance of stopping Tehran developing a nuclear bomb.

Deputy foreign ministers of the remaining parties to the Joint Comprehensive Plan of Action accord — Britain, China, France, Germany and Russia — will meet their Iranian counterpart on Friday in Vienna.