Russia says it has launched rocket strikes on Islamic State group targets in Syria from warships in the Caspian Sea – about 1,500km (930 miles) away.
Defence Minister Sergei Shoigu said four warships fired 26 sea-based cruise missiles on 11 targets, destroying them and causing no civilian casualties.
Meanwhile, Syrian ground troops have launched an offensive under Russian air cover, Syrian officials say.
Russia denies claims that its week of strikes have mainly hit non-IS targets.
The Syrian Observatory for Human Rights reported “the most intense fighting in months” in Hama and Idlib provinces. The clashes followed a wave of Russian air strikes in the same areas, it said.
It appears to be the first co-ordinated offensive since the air campaign by Russia – a staunch ally of Syrian President Bashar al-Assad – began on 30 September.
Russia says it is targeting “all terrorists”, but at least some of its air strikes have reportedly hit civilians and Western-backed rebels.
US Defence Secretary Ash Carter said that 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. We believe this is a fundamental mistake.”
Pentagon officials later revealed they had had to carry out at least one “safe separation” manoeuvre to avoid a US jet coming too close to a Russian aircraft over Syria. They said this happened after 1 October – without giving a specific date.
