RUSSIAN 'MEDDLING'

Since the start of US President Donald Trump's presidency, relations have been tainted by allegations of Russian interference in the 2016 US election and suspicions that the billionaire's campaign team colluded with the Kremlin.

Russia has denied any interference. Ahead of the summit, 12 Russian military intelligence agents were indicted for hacking Democrats during the election.

WAR IN UKRAINE

Along with its Western allies, the US accuses Moscow of providing military support to pro-Russian separatists fighting government forces in eastern Ukraine. Russia denies this.

Washington long resisted providing lethal weapons to Ukraine, fearing this could exacerbate the conflict, but in March the US approved a deal to sell anti-tank missiles to Kiev, angering Russia.

Mr Trump has made evasive comments on whether Washington might recognise Russia's annexation of Crimea from Ukraine.

SYRIA QUAGMIRE

Air strikes on Syria by the US and its allies in April last year and April this year, in response to alleged chemical attacks by President Bashar al-Assad's forces, have infuriated Russia.

In February, Moscow said a number of Russian civilians were killed by US-led coalition bombing. These were reportedly mercenaries fighting alongside pro-regime forces.

DISARMAMENT FEUDS

The US and Russia have accused each other of breaking international agreements over disarmament.

In March, President Vladimir Putin boasted Russia had developed new "invincible" weapons, including hypersonic missiles and unmanned submarines. In February, the Pentagon had called for a revamp of the US nuclear arsenal and development of new low-yield atomic weapons. Moscow condemned the new US nuclear policy as "bellicose" and "anti-Russian".

TENSIONS OVER NATO

Moscow views Nato's moves to beef up its eastern defences as aggressive steps aimed at encircling Russia.

Russia is also concerned at Nato plans launched in 2010 for a European missile shield that is due to be completed in 2020 with installations in Romania and Poland.

Mr Trump has lashed out at other Nato allies, urging them to spend more on defence.

IRAN NUCLEAR DEAL

Mr Trump's unilateral decision to pull out of the Iranian nuclear deal - signed in 2015 after lengthy negotiations - and to reimpose sanctions on Iran left both Russia and the West flabbergasted.

Russia, which has close ties both with Syria and Iran, has said European countries must "jointly defend their legal interests" in the deal.

NORTH KOREA

Russia reacted positively to a June 12 meeting in Singapore between Mr Trump and North Korean leader Kim Jong Un, where they signed a joint declaration but did not achieve any concrete breakthroughs on Pyongyang's nuclear activities.

Russian Foreign Minister Sergei Lavrov afterwards told state news agency RIA Novosti: "We very much hope that he (Mr Trump) starts the process of de-escalating tensions."

SPY POISONING

The United States this year joined in a wave of expulsions of Russian diplomats from various countries over the poisoning of a former Russian spy in Britain, which London blamed on Moscow.

TRADE WAR

Early this month, Russia raised import duties on some American imported goods in response to steep tariffs announced by the US on its steel and aluminium, as part of a global trade war.

AGENCE FRANCE-PRESSE