UPDATE 1-Russia eyes N. America meat ban over feed additive

* Wants imports certified free of ractopamine

* Frozen, chilled products face potential ban

* Russian export business worth $500 million annually (Adds details, background)

MOSCOW, Jan 28 (Reuters) - Russia warned on Monday it might soon bar imports of U.S. and Canadian beef and pork if producers do not certify them free of the feed additive ractopamine.

The potential ban could jeopardise more than $500 million a year of exports to Russia and coincides with mounting U.S.-Russian tensions over trade and human rights.

Alexey Alexeyenko, the spokesman for Russia's Veterinary and Phyto-Sanitary Surveillance Service (VPSS), said chilled products could be banned from Feb. 4 and frozen meat by Feb. 11.

Ractopamine is a growth stimulant used to make meat leaner which is banned in some countries because of concerns that residues could remain in the meat and cause health problems despite scientific evidence stating that it is safe.

The VPSS said last week it was considering tougher measures on U.S. and Canadian meat imports because they continued to arrive without certification requested by Russia.

An earlier statement left unclear whether frozen meat would be restricted. The VPSS had said it did not receive test results for chilled meat before it was sold. Alexeyenko said frozen meat was addressed in a separate letter to North American regulators.

Alexeyenko said the certification requirements are no more onerous on producers than regulations in place in the European Union. (Reporting by Melissa Akin; Editing by Lidia Kelly and David Cowell)