Spanish Defence Minister Pedro Morenes (left) and US Secretary of Defense Ashton Carter review the troops in Madrid on Monday.

AFP/Madrid

US Defence Secretary Ashton Carter said on Monday that Russia is pursuing a "losing strategy" in Syria and that it must live up to its commitments in Ukraine.

Speaking in Madrid at the start of a five-day trip to Europe, Carter told Spanish military officials that by carrying out bombing in Syria, Russia had only worsened the 4.5-year-old conflict.

Russia last week started air strikes in Syria. Moscow claimed it was hitting Islamic State jihadists, but the Pentagon says Russian jets are targeting rebel groups in order to support the regime of President Bashar al-Assad.

"Russia has escalated the civil war, putting further at risk the very political resolution and preservation of Syria's structure of future governance it says that it wants," Carter said at the Center for Strategic Studies and Defence.

"It remains my hope that Vladimir Putin will see that tethering Russia to a sinking ship is a losing strategy, and will decide to confront the threat presented by (IS) instead of continuing its unilateral airstrikes against Assad's opposition."

Carter's trip is aimed at acknowledging allies in the 60-plus member US-led coalition that is carrying out daily drone and plane strikes against IS jihadists in Iraq and Syria.

Europe is struggling to deal with the refugee crisis sparked by the Syrian conflict, which has uprooted millions of people.

Carter also is attending a Nato summit in Brussels on Thursday, where several items including Russia's stance in eastern Ukraine will be discussed.

"We will continue to make it clear that if Russia wants to end its international isolation and be considered a responsible global power, it must stop its aggression in eastern Ukraine, end its occupation and attempted annexation of Crimea, and live up to its commitments under the Minsk agreements," Carter said.

"We will take all necessary steps to deter Russia's malign and destabilising influence, coercion, and aggression, including its efforts to undermine strategic stability and challenge the military balance in Europe."

Russian military says it struck nine IS targets

Russian military jets carried out strikes on nine Islamic State sites in Syria over the past 24 hours, the defence ministry in Moscow said on Monday.

The Russian warplanes hit IS command centres, weapon caches, artillery and communication posts in the Homs, Idlib and Latakia provinces of Syria, the ministry said in a statement.

"Twenty-five sorties were completed by Su-34, Su-24 and Su-25 jets from the airbase in Hmeimim. Nine IS facilities were struck," the statement said.

In the northwestern Idlib province the Russian military said it had destroyed a training camp by the city of Jisr al-Shughur, artillery positions near Jabal al-Qobeh and armoured vehicles.

A command centre in the coastal region of Latakia was also hit, while in the Homs province a command centre near the town of Rastan was struck along with two ammunition depots and a communication centre, Moscow said.