WASHINGTON: US President Donald Trump on Wednesday called on Russia to rein in Syrian President Bashar al-Assad and his key ally Iran, as Washington and Moscow sought to boost their fragile ties with high-profile White House talks.

Russian Foreign Minister Sergei Lavrov, the highest-ranking Russian official to visit Washington since Trump came to power in January, earned a rare invitation to the Oval Office for a head-to-head with the Republican president.

Before visiting the White House, Lavrov huddled with US Secretary of State Rex Tillerson to discuss the crises in Syria and Ukraine -- talks qualified by the veteran Russian diplomat as "constructive."

The meetings were nevertheless somewhat overshadowed by the uproar in Washington over Trump's firing of FBI chief James Comey -- the man who was leading a probe into Russia's alleged meddling in the US presidential election.

"We had a very, very good meeting" Trump said shortly after seeing Lavrov. "We're going to stop the killing and the death (in Syria)."

The Republican leader nevertheless told Lavrov that Moscow should "rein in the Assad regime, Iran and Iranian proxies," the White House said.

Lavrov, who came to Washington seeking US support for a Russian plan to create safe zones in Syria, said "concrete mechanisms that we can manage together" were discussed.

"Today, we have a common understanding that, as active players in the diplomatic process regarding Syria, we are going to pursue these contacts together and with other key countries, especially those in the region," he said.

Trump's critics cried foul over the White House invitation to Lavrov, whose government stands accused by US intelligence agencies of interfering in the November election, which Trump won over Democrat Hillary Clinton.

Democrats have seen Comey's shock dismissal as an assault on an investigation that could have sweeping repercussions for his administration.

Lavrov, who last set foot in Washington in August 2013, dismissed all claims of election meddling as "fabrications," preferring in his press conference to focus on the substance of his meetings.

"President Trump clearly confirmed his interest in building mutually beneficial, business-like pragmatic relations," he told journalists.

Earlier, when Lavrov arrived at the State Department to meet Tillerson, he cracked a joke about Comey's firing, answering shouted questions from reporters by saying: "Was he fired?... You're kidding, you're kidding!"

- Tense ties -

In Moscow, Russian President Vladimir Putin met Wednesday with his security council to discuss US-Russian relations in the context of Lavrov's meeting with Trump, Kremlin spokesman Dmitry Peskov told the RIA Novosti news agency.

Relations between the two former Cold War foes soured under former president Barack Obama over Russia's annexation of Crimea in 2014 and its unyielding support for Syrian President Bashar al-Assad.

Since March 2011, the Syrian conflict has caused more than 320,000 deaths and forced millions of refugees to flee.

Neither Washington, which backs the opposition, nor Moscow, a longtime ally of the Syrian regime, have managed to find a solution to the conflict.

Since the end of Obama's presidency in January, the United States has gradually withdrawn from the diplomatic process, leaving Russia to take the lead.

 - 'De-escalation zones' -

The agreement calls for the creation of four "de-escalation zones" to shore up a ceasefire, ban flights and allow for humanitarian aid deliveries.

Washington has given the deal a skeptical welcome, citing concerns about Tehran's role as a guarantor even as it expressed hope the agreement could set the stage for a later settlement.

"We will look at the proposal, see if it can work," Pentagon chief Jim Mattis said Monday.

Several ceasefires have been agreed on since Syria's conflict broke out, but they have failed to stem the fighting.

Over the past six years, Moscow and Washington have sparred multiple times over the conflict in Syria, especially concerning Assad's fate.

Trump's arrival to power has not brought the two sides closer -- and in early April, the US even launched direct military action against the Syrian regime in retaliation for an apparent chemical attack.

Both countries have recently indicated that relations under Trump have never been so bad, though Wednesday's meetings appeared rather cordial.

Trump "emphasized his desire to build a better relationship between the United States and Russia," the White House said.

 - 'Common position' -

On the conflict in Ukraine, the White House said Trump had "stressed Russia's responsibility to fully implement the Minsk agreements."

The State Department added: "Sanctions on Russia will remain in place until Moscow reverses the actions that triggered them."

After Wednesday's talks, Lavrov and Tillerson will again meet Thursday in Alaska for the Arctic Council meeting, an intergovernmental forum for cooperation on the environment, oil and mining, shipping, fisheries and tourism.

It brings together the eight countries bordering the Arctic Ocean -- Canada, Denmark, Finland, Iceland, Norway, Sweden, Russia and the United States.

Tillerson and Lavrov's meeting in Alaska comes 150 years after Washington purchased the US state from Moscow.-AFP