Diplomatic relations between Russia and the United States are the most difficult they have been since the end of the Cold War, the Russian foreign ministry has said.

The warning comes ahead of a visit to the country by Donald Trump's chief diplomat Rex Tillerson.

Tensions between the two countries have soared over the conflict in Syria, with Russian President Vladimir Putin backing Syria's government and the US opposing it.

Mr Trump launched cruise missile strikes on a Syrian regime airbase last week after reports that government forces had launched a gas attack against civilians, including children.

"It's clear Russian-US relations have never been so difficult since end of Cold War," the Russian foreign ministry said in a statement.

The ministry said it was concerned about many aspects of US foreign policy, including on Libya, Yemen and Syria, but said it was particularly concerned about North Korea. "We are really worried about what Washington has in mind for North Korea after it hinted at the possibility of a unilateral military scenario. "It's important to understand how that would tally with collective obligations on de-nuclearising the Korean peninsula, something that is underpinned in UN Security Council resolutions."

US/South Korea joint exercise Operation Pacific Reach Show all 10 1 /10 US/South Korea joint exercise Operation Pacific Reach US/South Korea joint exercise Operation Pacific Reach US Marine soldiers patrol during the US-South Korea joint Exercise Operation Pacific Reach in Pohang, South Korea. North Korea is vowing tough counteraction to any military moves that might follow the US move to send the USS Carl Vinson aircraft carrier and its battle group to waters off the Korean Peninsula AP US/South Korea joint exercise Operation Pacific Reach South Korean soldiers take part in the Operation Pacific Reach joint logistic exercise in Pohang, South Korea Reuters US/South Korea joint exercise Operation Pacific Reach North Korea is vowing tough counteraction to any military moves that might follow the US move to send the USS Carl Vinson aircraft carrier and its battle group to waters off the Korean Peninsula AP US/South Korea joint exercise Operation Pacific Reach South Korean marine soldiers stand guard during the US-South Korea joint Exercise Operation Pacific Reach in Pohang, South Korea AP US/South Korea joint exercise Operation Pacific Reach A US Marine takes part in Operation Pacific Reach joint logistic exercise in Pohang, South Korea Reuters US/South Korea joint exercise Operation Pacific Reach A US Marine takes a position during a Combined Joint Logistics Over-the-Shore (CJLOTS) exercise as part of a joint defence exercise at a beach in Pohang Getty Images US/South Korea joint exercise Operation Pacific Reach South Korea and the United States kicked off a combined distribution exercise focused on integrating the two sides alliance logistics capabilities, in Pohang, 260 kms southeast of Seoul Getty Images US/South Korea joint exercise Operation Pacific Reach South Korea and the United States kicked off a combined distribution exercise focused on integrating the two sides alliance logistics capabilities Getty Images US/South Korea joint exercise Operation Pacific Reach A US Marine walks past a military vehicle during a Combined Joint Logistics Over-the-Shore (CJLOTS) exercise as part of a joint defence exercise in Pohang Getty Images US/South Korea joint exercise Operation Pacific Reach US Marines gather at a beach during a Combined Joint Logistics Over-the-Shore (CJLOTS) exercise as part of a joint defence exercise in Pohang, 260 kms southeast of Seoul, South Korea Getty Images

Mr Tillerson, the US secretary of state, says he is visiting Russia to develop "a solution which will deliver a lasting political settlement" to the Syrian civil war.

UK Foreign Secretary Boris Johnson cancelled a visit of his own last week to make way for the US diplomat, prompting suggestions from domestic politicians and the Kremlin that he is a US "poodle".

Russian Foreign Minister Sergei Lavrov said ahead of the meeting that he is hoping for productive talks with Mr Tillerson and that he would like to know what the USA plans to do in Yemen and Libya.

A Downing Street spokesperson said Prime Minister Theresa May and US President Donald Trump had spoken by telephone and “agreed that a window of opportunity now exists in which to persuade Russia that its alliance with Assad is no longer in its strategic interest”.