The aftermath of the fall of the USSR initially saw a rare period of cooperation, including over the NATO military alliance, but strains appeared soon afterwards.

Here is a reminder of a difficult relationship that has been key to world affairs.

- Kosovo war -

In 1999 NATO launches a 78-day bombing campaign on Yugoslavia to force its republic of Serbia to withdraw forces from Kosovo where it is accused of repressing separatists.

Russia, an ally of Serbia, had threatened a return to a Cold War-style freeze in relations if NATO acted.

Two days after the strikes start, Russia kicks out NATO's representative and suspends military cooperation.

Tensions resurface after Kosovo's 2008 declaration of independence, not recognised by Russia.

- NATO grows east -

In March 1999 NATO admits three former members of the Soviet-era Warsaw Pact -- the Czech Republic, Hungary and Poland.

Moscow warns NATO against allowing former Soviet republics to join but in 2004 it welcomes Estonia, Latvia and Lithuania, along with ex-communist states Bulgaria, Romania, Slovakia and Slovenia.

Their eventual inclusion into the European Union also annoys Russia.

- Missile shield -

Moscow's suspicions towards NATO's tilt eastwards deepen with plans launched in 2010 for a European missile shield to counter a perceived threat from Iran.

To be operational by 2020, it includes the deployment of missile interceptors and powerful radars in Poland and Romania.

- Georgia conflict -

In August 2008 Russia bombs the Georgian capital Tbilisi after it intervened in the Georgian separatist region of South Ossetia, and occupies a large part of the former Soviet republic's territory, provoking a Western outcry.

A peace accord negotiated by French president Nicolas Sarkozy leads to the withdrawal of Russian troops. However Moscow recognises separatist South Ossetia and Abkhazia and maintains a heavy military presence in both.

After the war, NATO freezes relations with Moscow until the following June. Moscow then suspends its military cooperation with NATO.

- Ukraine crisis-

Russia in 2014 annexes Ukraine's Crimea peninsula and is accused by the West of backing separatists waging an insurgency.

Washington and Europe impose painful economic sanctions.

NATO suspends civilian and military cooperation with Moscow and the allies put their troops on a state of alert, with battalions deployed in Poland and the ex-Soviet Baltic states.

- Suspicions of US vote meddling -

Accusations of Russian interference in the 2016 US presidential election sour relations between the two countries.

The claims include suspicion of collusion between Donald Trump's campaign and the Kremlin.

In February 2018, 13 Russians are indicted by Washington for using online posts to influence opinion in favour of Trump.

- Spy poisoning in Britain -

London blames Moscow for the March 8, 2018 poisoning of former Russian double agent, Sergei Skripal, and his daughter in England.

Moscow strongly denies involvement.

Western allies back Britain and expel more than 150 Russian diplomats; Moscow responds by expelling the same number of Western envoys.

- Syria -

Russia and the West are on opposing sides in Syria's seven-year war, with Moscow supporting President Bashar al-Assad while Western-backed rebels are seeking to unseat him.

Russia uses its veto 12 times against UN Security Council resolutions on the Syrian crisis.

Since 2015 it has carried out a campaign of air strikes in support of Assad.

In 2017 US President Donald Trump orders air strikes against a Syrian airbase after a chemical attack on the rebel-held town of Khan Sheikhun.

It leads Russia to suspend a hotline with the US army on Syria operations.

In February 2018 the US-led coalition bombs pro-regime fighters in the Syrian province of Deir Ezzor, reportedly killing several Russian mercenaries.

The United States, Britain and France carry out a wave of strikes against Assad's regime on April 14, a week after a suspected deadly gas attack on the rebel-held Damascus suburb of Douma.

The US chairman of the Joint Chiefs of Staff said the targets of the strikes were chosen to avoid hitting Russian military assets.

However Russia's ambassador to the US, Anatoly Antonov, warns of unspecified repercussions, adding that "insulting" Putin was "unacceptable".