Putin told leaders of the six-nation Collective Security Treaty Organisation (CSTO) on Monday that militants fighting Assad could eventually expand attacks beyond Syria and the Middle East.

"The militant groups (in Syria) did not come out of nowhere, and they will not vanish into thin air," Putin said.

"The problem of terrorism spilling from one country to another is absolutely real and could directly affect the interests of any one of our countries," he said, citing the deadly attack on a shopping mall in Nairobi as an example.

"We are now witnessing a terrible tragedy unfold in Kenya. The militants came from another country, as far as we can judge, and are committing horrendous bloody crimes," Putin said at a CSTO summit in the Russian Black Sea resort city of Sochi.

His words appeared to be a warning about violence spreading from both Syria and Afghanistan, which shares a long border with CSTO member Tajikistan in Central Asia. The security alliance also includes Kazakhstan, Kyrgyzstan, Armenia and Belarus.

Russian officials have expressed concern that Russian-born militants fighting in Syria could return to Russia's North Caucasus and join an insurgency that claims lives almost daily.

They have also voiced worries that violence could spread into former Soviet Central Asia and Russia after the withdrawal of most Western troops from Afghanistan by the end of next year.

Russia has also warned the West that military intervention in Syria would play into the hands of the militants.

NJF/NJF