A recently unveiled Russian plan to stabilize Syria after more than six years of civil war is the most urgent foreign policy topic on the agenda, according to The Associated Press.

Both governments have said they want to end a civil war that has killed up to 400,000 people and allowed the self-proclaimed Islamic State (IS) to emerge as a global terror threat.

The continued fighting between rebels and the Moscow-backed Syrian president Bashar al-Assad's military has complicated US efforts to defeat IS.

A plan is a plan

Lavrov arrives in the US capital after discussing an agreement with Iran and Turkey last week.

The plan focuses on the creation of four de-escalation zones, which would not cover areas where the US-led coalition is fighting IS.

Details still need to be finalized and the US response has been cautious, Defense Secretary Jim Mattis saying administration officials are still studying the concept and its various unanswered questions.

Watch video 00:33 Syrian 'safe zone' deal comes into effect

Best of enemies?

The meeting will be the highest-level contact between Trump and the government of Russian President Vladimir Putin since Trump took office on January 20.

Lavrov hasn't visited Washington at all since 2013, a year before Russia's annexation of Ukraine's Crimea region and two years before it intervened militarily in Syria to help Assad remain in power.

Relations apparently deteriorated between the US and Russia after US air strikes hit a Syrian airfield in April in response to a chemical weapons attack that Washington blamed on Assad.

The meeting could signal that the two governments have improved ties that Trump recently described as being at an "all-time low."

Lavrov will meet earlier in the day with Secretary of State Rex Tillerson, The Associated Press learned.

Russian connection not going away

The meeting will be hard to separate from the unfolding political drama in Washington.

FBI and congressional investigations are looking into possible collusion between Trump campaign associates and the Kremlin related to last year's presidential election.

US intelligence agencies accuse Moscow of meddling to help Trump's chances of victory.

On Tuesday Trump abruptly fired FBI Director James Comey, ousting the nation's top law enforcement official amid the FBI's investigation into Trump's ties with Russia.

In January, Trump fired his national security adviser, Michael Flynn, saying Flynn had misled senior administration officials about his pre-inauguration talks with Sergey Kislyak, Russia's ambassador in Washington.

In a Senate hearing Monday, former acting Attorney General Sally Yates said she had "bluntly warned" Trump's White House in January that Flynn "essentially could be blackmailed" by the Russians because he apparently had lied about his contacts with Kislyak.

Trump has said he has no ties to Russia and isn't aware of any involvement by his aides in any Russian election interference. He calls the various investigations a "hoax" driven by Democrats.

jbh/kl (Reuters, AP)