"We are not going to force Iranians out of Syria. We don’t even think the Russians can force the Iranians out of Syria because force implies force, military action," US Special Representative for Syria Engagement James Jeffrey said on the sidelines of the UN General Assembly on Thursday.

"This is all about political pressure" and "technically this is the Syrian government that has invited the Iranians in," he noted.

However, he added, "It is our expectation that the Syrian government… at the end of the political process or at some point of the politics process will no longer feel the need to have the Iranian forces there."

Jeffrey added that the US president wanted the American troops to remain in Syria until Iranians left the Arab country.

However, the US is not necessarily American boots on the ground, he went on to say.

"There are many ways that we can be on the ground. We're certainly on the ground diplomatically," he said, while adding that no options were definite.

John Bolton, Trump's national security adviser, earlier on Monday said the American forces were not going to leave Syria "as long as Iranian troops are outside Iranian borders."

At the request of Damascus, Iran has been providing military advisory assistance to the Syrian government forces who are fighting an all-out foreign-sponsored militancy.

Iran's military presence in Syria is a thorn in the side of Israel. Tel Aviv and its main ally the US want Syria to ask Iranian advisers to leave the country and dismantle what it claims to be Iranian military bases. 

In an interview with the al-Alam News Network in June, Assad said Iran does not have any military bases in Syria, but if there is “a need for Iranian military bases, we will not hesitate."

Assad said Damascus had invited Iran and Russia to Syria, unlike the American, French, Turkish and Israeli troops who are occupying forces.