MOSCOW (Reuters) - Russia has reinforced its air base in Syria with several bombers and is ready to send ground attack aircraft as it intensifies support for Syrian government troops after the collapse of a ceasefire plan, Russia's Izvestia daily reported on Friday (Sept 30).

A group of Su-24 and Su-34 frontline bombers have already arrived at the Hmeymim base, Izvestia wrote, quoting an unnamed military official.

"If need be, the air force group will be (further) built up within two to three days," he said. "Su-25 ground attack fighters designated to be sent to Hmeymim have already been selected in their units and their crews are on a stand-by, awaiting orders from their commanders."

Russia's defence ministry did not immediately respond to a request from Reuters for comment.

U.S. Secretary of State John Kerry on Thursday said there is no point pursuing further negotiations with Russia over Syria, leaving Washington without a backup plan and scrambling to develop new options to stop the mounting carnage.

As the US-Russian ceasefire plan for Syria fell through, US officials have told Reuters that President Barack Obama's administration had begun considering tougher responses - including military options - to the Russian-backed Syrian government's assault on Aleppo, the country's largest city.

The Su-25 is an armoured twin-engine jet which was battle-tested in the 1980s during the Soviet war in Afghanistan. It can be used to strafe targets on the ground, or as a bomber.

Russian President Vladimir Putin ordered a partial pullout of warplanes and servicemen from Hmeymim in March, saying at the time that the Kremlin had achieved most of its objectives, but stressing it could fast build up its forces again if needed.