On the seventh anniversary of the Syrian conflict, National Security Adviser HR McMaster said Russia is “complicit” in the violence in Syria and should be held responsible for “providing political cover” for the “atrocities” of President Bashar al-Assad’s regime.

Speaking at the Holocaust Museum in Washington DC, Mr McMaster’s fiery address also held Iran accountable for its role in the bloody conflict that has resulted in over 400,000 people dead and up to 13 million Syrians displaced within and outside of the country.

His comments about Russia come during a tense time when rumours have swirled about his possible sacking by President Donald Trump and a new round of sanctions placed on Russian nationals for suspected meddling in the 2016 US election.

He also noted that Moscow has carried out a hundred bombing missions in the besieged eastern Ghouta area near the capital of Damascus.

He also cited the recent poisoning of former Russian Sergei Skripal and his daughter Yulia in Salisbury as a sign of an increasingly aggressive Kremlin.

“If Iran and Russia do not stop enabling the regime’s atrocities and adhere to [United Nations] Security Council resolutions, all nations must respond more forcibly than simply issuing strong statements,” he said.

Mr McMaster called for “serious political and economic consequences” on both countries. He noted that Mr Assad “should not have impunity for his crimes, and neither should his sponsors”.

He invoked the venue as a plea for action to end the conflict in Syria and also listed the ways the US has helped Syrian refugees, but left out Mr Trump’s travel ban.

UN Security Council unanimously backs ceasefire in Syria

“We know that these horrors can happen again..but remembrance is only the first step. We cannot stop at remembrance alone. If we are to fulfill our promise — ‘Never again’ — we must also act to protect victims and hold all responsible parties accountable. Unfortunately, today, in Syria, we are confronted once more with some of the worst atrocities known to man,” he said.

However, whether Mr McMaster has any sway in the administration remains to be seen as another member of the Cabinet who had been at odds with the President over a number of issues, Rex Tillerson, was recently fired via Twitter.

The latest issue was Russia’s involvement in the poisoning of the former spy in the UK.

While UK Prime Minister Theresa May was quick to blame the Russians for the incident, calling it a "brazen" act, expelling 23 Russian diplomats, and cutting high-level contact with Moscow for the attack on UK soil - Mr Trump was more cautious initially.

Turkish attack on Afrin, northern Syria – in pictures Show all 9 1 /9 Turkish attack on Afrin, northern Syria – in pictures Turkish attack on Afrin, northern Syria – in pictures Smoke billows following a Turkish airstrike on a village in the Afrin district, on 28 January, 2018. Turkey launched operation "Olive Branch" on January 20 against the Kurdish People's Protection Units (YPG) militia in Afrin, supporting Syrian opposition fighters with ground troops and air strikes AFP Turkish attack on Afrin, northern Syria – in pictures Smoke billows from surrounding villages during the Turkish military operation against the Kurdish enclave on 28 January, 2018 AFP/Getty Turkish attack on Afrin, northern Syria – in pictures Twenty-year old Kifah al-Moussa, a Syrian Arab woman living among the Kurds of Afrin province, was working on a chicken farm in the village of Maryameen when a Turkish aircraft bombed the building at midday on 21 January, wounding her in the chest. When she recovered consciousness, she found eight people from one family lying dead around her Yara Ismail Turkish attack on Afrin, northern Syria – in pictures Mohamed Hussein, a 58-year-old Kurdish farmer, lies in the Afrin hospital, wounded in the head and eye after his home was bombed by Turkish aircraft on the second night of the attack Yara Ismail Turkish attack on Afrin, northern Syria – in pictures Syrian Kurds sit on benches overlooking a street in Afrin, on 28 January, 2018. Above is a memorial to ‘martyrs’ who died in the fight against Isis AFP/Getty Turkish attack on Afrin, northern Syria – in pictures Smoke is seen rising on the Syrian side of the border, at Hassa, near Hatay, southern Turkey as Turkish jet fighters hit People's Protection Unit (YPG) positions, on 28 January, 2018 AFP/Getty Turkish attack on Afrin, northern Syria – in pictures A Turkish made T-155 Firtina (Storm) howitzer is dispatched to the border at Hassa near Hatay, southern Turkey, on 28 January, 2018 AFP/Getty Turkish attack on Afrin, northern Syria – in pictures A Turkish soldier waves a flag on Mount Barsaya, northeast of Afrin, on 28 January, 2018 Reuters Turkish attack on Afrin, northern Syria – in pictures Turkey-backed Free Syrian Army fighters are seen in Barsaya mountain, northeast of Afrin, on 28 January, 2018 Reuters

He said on Tuesday that "as soon as we get the facts straight, if we agree with them, we will condemn Russia or whoever it may be".

However, Mr Tillerson joined in supporting the US ally and called the poisoning “a really egregious act” that appears to have “clearly” come from Russia. He had called President Vladimir Putin's country "an irresponsible force of instability in the world, acting with open disregard for the sovereignty of other states and the life of their citizens".

It was not until after US Ambassador to the United Nations Nikki Haley said during a Security Council meeting that the US "stands in absolute solidarity" with the UK, that the White House issued a statement echoing the sentiment.

Press Secretary Sarah Huckabee Sanders said in the late Wednesday evening statement that "Russia is responsible for the reckless nerve agent attack".