Russia's growing military involvement in the Syria conflict is expected to be high on the agenda of Nato defence ministers meeting in Brussels. It comes after Nato member Turkey said Russian jets had violated its airspace. Russia has fired missiles from a warship in addition to air strikes to support Syrian leader Bashar al-Assad. But Moscow denies Western accusations that its strikes have mainly hit Assad opponents, some supported by the West, and not Islamic State (IS) militants.

BBC defence correspondent Jonathan Marcus says Nato aims to make clear it will respond to any challenge.

On Thursday, Nato Secretary-General Jens Stoltenberg said the alliance had expressed its concern over Russia's "strong and increased military presence" in Syria. He called on Moscow to play a "constructive and co-operative role" to fight IS and to stop supporting Mr Assad. But he added that the situation underlined the need for political initiatives to end Syria's war. Nato ministers are expected to express their solidarity with Turkey. They will also address increased concern among Baltic member states following Russia's involvement in eastern Ukraine. UK Defence Secretary Michael Fallon is expected to announce that Britain is ready to make a long-term troop deployment to the Baltic republics, our correspondent says. But, he adds, ministers are meeting amid a deepening sense of crisis. On Wednesday, Russia said it had launched missile strikes against IS from warships in the Caspian Sea - about 1,500km (930 miles) away.

Russia's foreign ministry also said Moscow was willing to establish contact with the Free Syrian Army - a Western-backed rebel group - to discuss fighting IS "and other terrorist groups". But US Defence Secretary Ash Carter said coalition forces fighting IS in Syria would not co-operate with Russia. "We believe Russia has the wrong strategy," he said. "They continue to hit targets that are not IS."