Russia and Syria should face war crimes probe for civilian attacks, says Kerry

Russia and Syria should face a war crimes investigation for their attacks on Syrian civilians, according to US secretary of state John Kerry, further illustrating the downward spiral in relations between Washington and Moscow.

Mr Kerry said Syrian forces hit a hospital overnight, killing 20 people and wounding 100, in what would be the latest strike by Moscow or its ally in Damascus on a civilian target.

"Russia and the regime owe the world more than an explanation about why they keep hitting hospitals, and medical facilities, and women and children," Mr Kerry told reporters alongside French foreign minister Jean-Marc Ayrault, who arrived in Washington directly from meeting Russian officials in Moscow.

Mr Kerry (pictured) said such acts "beg for an appropriate investigation of war crimes".

"They are beyond the accidental now, way beyond," he added said in some of his toughest criticism to date. He accused Russia and Syria of undertaking a targeted strategy to "terrorise civilians".

Mr Ayrault spoke of a new French effort for a ceasefire in Syria, but it is unclear what advantages his plan would have over the US-Russian led process that collapsed last month.

Mr Kerry's September 9 agreement with Russian foreign minister Sergey Lavrov would have created a new counter-terrorism alliance in Syria, if fighting had stopped for a week and aid deliveries been permitted to reach desperate civilians in rebel-held parts of Aleppo and other besieged areas.

Neither condition was met.

The truce then broke completely when Syria and Russia renewed their military offensive in Aleppo.

Mr Kerry ended bilateral discussions with Moscow on the military partnership earlier this week.

The war has killed as many as half a million people since 2011, contributed to Europe's worst refugee crisis since the Second World War and allowed Islamic State to carve out territory for itself and emerge as a global terror threat.

As Mr Kerry and Mr Ayrault spoke, Russia's lower house of parliament ratified a treaty with Syria that allows the Russian military to stay indefinitely in the Middle Eastern country.

The Kremlin-controlled State Duma voted unanimously to ratify the deal, which formalises Moscow's military presence at the Hemeimeem air base in Syria's coastal province of Latakia.

The move comes as a show of support for embattled Syrian president Bashar Assad, and allows Russia to use the base free of charge and for as long as it requires.

Russia launched an air campaign in Syria a year ago, reversing the tide of war and helping Assad's forces win back key ground. Moscow says its goal is to help the Syrian army fight terrorism.

Russia also has a naval base in Syria's port of Tartus.