Fighting between Syrian government forces backed by Russian air power and Turkish forces and Syrian rebels is pulling Moscow and Ankara more into the country's civil war.

A fierce battle for the last region held by rebels opposing President al-Assad's forces left 27 fighters dead on February 20, the Syrian Observatory for Human Rights reported.

At least 11 pro-government combatants and 14 on the pro-Turkey side were killed as well as two Turkish soldiers.

The fighting took place near the northwestern region of Idlib in Syria and involved Russian warplanes, Russian and Turkish officials said.

The Russian Air Force carried out the strikes with Su-24 bombers, the Russian Center for the Reconciliation of Warring Sides said in a statement the same day.

In turn, Turkey, a NATO member allied with the militants, retaliated.

The Turkish Defense Ministry claimed that as many as 50 Syrian government soldiers were killed in response, and that two armored personnel carriers, and other equipment were destroyed.

Both sides claimed they defeated the other in the February 20 clashes.

The escalation was followed by Turkish Defense Minister Hulusi Akar saying there should be "no doubt" Ankara will activate S-400 missile systems bought from Russia.

The clashes in Idlib, the last region held by rebels resisting Syrian-government forces, come a day after Turkish President Recep Tayyip Erdogan warned of an imminent Turkish offensive in the area.

Thirteen Turkish soldiers were killed in Syrian attacks earlier this month, prompting Erdogan to warn of future action should another Turkish soldier be harmed.

Speaking in Geneva, the UN refugee chief called for the fighting to end to allow hundreds of thousands of trapped civilians to move to safer areas.

The UN says that since December, 800,000 people have been displaced due to fighting in the area.

The civil war has killed more than 400,000 people and displaced millions since it began with a crackdown on anti-government protesters in March 2011.

Based on reporting by Reuters, AP, TASS, AFP, and Interfax

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