Russian Foreign Minister Sergey Lavrov has said the United States "does not want to keep Syria as a state in its current borders", accusing Washington of seeking to establish a Kurdish-controlled entity along Turkish and Iraqi border zones.

Speaking at an annual press conference in Moscow to review the past year's diplomatic activities on Monday, Lavrov also said Russia would not support Washington's attempts to change the Iran nuclear deal.

"The [US'] actions that we have been observing indicate that the US does not want to keep Syria as a state in its current borders ... The US wants to help the Syrian Democratic Forces to set up some border security zones," he said, referring to a US-backed rebel alliance dominated by Syrian Kurds, known as the SDF.

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"What it would mean is that vast swaths of territory along the border of Turkey and Iraq would be isolated, it's to the east of the Euphrates river. There are difficult relations between Kurds and Arabs there. If you say that this zone will be controlled by the forces supported by the US, there will be a force of 30,000 people."

Lavrov said that the development would be "a very big deal" raising "a lot of question marks".

"There is a fear that they are pursuing a policy to cut Syria into several pieces," he said.

"But again, there is nothing in the UN Security Council resolutions that have been pointing to that and neither is it in our previous agreements, so we are expecting some clarification from the US on that."

'Blatant assault'

Shortly after his comments, the Syrian government denounced a new border force the US is building with the SDF in northern Syria as a "blatant assault" on sovereignty.

"What the American administration has done comes in the context of its destructive policy in the region to fragment countries ... and impede any solutions to the crises," state news agency SANA cited an official source in the ministry as saying.

Also at Monday's news conference, Lavrov said the collapse of the Iran nuclear deal would negatively impact a dialogue with North Korea.

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"We will seek to maintain the agreements on the Iranian nuclear programme ... We will continue our efforts to make the US accept the reality. The reality is that Iran has been fulfilling all its obligations under the JCPOA, which has been regularly verified by the IAEA director general," he said.

He was referring to the Joint Comprehensive Plan of Action (JCPOA) - the nuclear deal signed in 2015 between Iran, the US, China, UK, France, Germany and Russia as well as the European Union.

Trump said last week he would waive nuclear sanctions against Iran for the last time to give Washington and its European allies a chance to fix the "terrible flaws" of the nuclear deal.