Secretary of Defense Ashton Carter said on Tuesday the Obama administration is stepping up its military campaign against the 'Islamic State' (IS) militant group.

In testimony before the Senate Armed Services Committee, the Pentagon chief told senators that US and coalition forces would intensify their air strikes in the region, focusing specifically on the IS-held cities of Raqqa in Syria and Ramadi in Iraq. US forces would also improve training for Arab forces fighting IS on the ground.

Carter added that the US would target the group's oil infrastructure, its main source of financial security.

Torn over Assad

The decision comes as Russian-backed government forces in Syria have also stepped up their offensive against IS. Most recently, government soldiers fought to take back a key supply line south of Aleppo, which is being held by the terror group.

The US and Russia have sought to reach a consensus over Syria, but conflicting goals in the region have prevented much headway from being made. Moscow supports Syria's embattled president, Bashar al-Assad, whereas Washington wants to see him removed.

Iranian-Russian phone call

Russia's foreign ministry said Tuesday that Russian Foreign Minister Sergei Lavrov and Iranian Foreign Minister Mohammad Javad Zarif had had a phone conversation on ways to resolve the Syria crisis.

The Russian ministry said urgent measures should be taken to improve political dialogue within Syria, and that all the main countries in the region should be involved in that process.

Earlier this week, Lavrov said his country would consider supporting the Free Syrian Army, a rebel group fighting both IS and Assad, but his proposal was swiftly rebutted by certain opposition members.

Since launching its military intervention in Syria in late September, Russia has been criticized for targeting "moderate" rebel groups as well as IS militants, something Moscow denies. This past weekend, Moscow said it carried nearly 100 sorties and destroyed more than 800 militant targets.

blc/ng, ipj (AP, dpa, Reuters)