Moscow (AFP) - A Russian military adviser has been killed in Syria by shelling from the Islamic State group, the Russian defence ministry told Ria Novosti news agency Wednesday.

The officer was training Syrian soldiers loyal to President Bashar al-Assad in the use of "new weapons" when he was "fatally wounded" on Monday, the ministry was quoted as saying. No details were given about where the attack took place.

The Syrian Observatory for Human Rights, a British-based monitoring group with a network of sources on the ground in Syria, said three Russian soldiers were also wounded in the attack, which it said took place in an area where IS does not have a presence.

The military adviser is the third Russian officer to have been killed since Moscow began its military intervention in the war-torn country in late September.

The Russian government has launched a massive air campaign in Syria against rebels fighting to overthrow Assad, a long-time Moscow ally, but it says no Russian troops are fighting on the ground.

The Observatory said Wednesday's incident took place in the northwestern province of Latakia, where it says rebel groups fighting against the regime operate, but not IS.

Russian Foreign Minister Sergei Lavrov said earlier Wednesday the country would press ahead with its bombing campaign in Syria until "terrorist organisations" such as the Islamic State jihadist group are defeated.

Russia suffered its first casualties in the conflict in November, when Turkey shot down a Russian fighter jet it claimed had violated Turkish airspace. One of the two pilots on board died in the downing. Another serviceman was killed in a subsequent rescue mission.

The incident triggered a huge row between the countries, with Turkey saying the jet strayed into its airspace and ignored repeated warnings, and Moscow insisting it did not cross over from Syria and accusing Ankara of a planned provocation.

Backed by the intense Russian air campaign, Syrian troops have been gaining ground in recent weeks. On Wednesday, Assad's regime cut the last supply route linking rebels in Aleppo to the Turkish border, in a major blow to the opposition.

The development was followed by the announcement that troubled talks in Geneva aimed at securing peace in Syria were being suspended until February 25.