MOSCOW (Reuters) - Russian President Vladimir Putin called on Saturday for improvement of Moscow's secret services to tackle "modern challenges and threats" amid his country's standoff with the West over the Ukrainian crisis.

The call came in a letter by Putin, himself a former KGB agent, to veterans and current operatives of Russia's security services on the day Moscow traditionally honors them.

"I stress that modern challenges and threats and emergence of new destabilizing factors require an increase in the efficiency of the whole system of domestic special services," Putin said, according to the letter released by the Kremlin.

The key tasks for Russia's secret operatives are to fight international terrorism and "any attempts of foreign special services to deal a blow to Russia (and) her political and economic interests," he said.

The European Union and the United States have imposed wide-ranging economic sanctions and visa bans against Russian individuals and companies over Moscow's role in the conflict in eastern Ukraine and its annexation of the Crimea peninsula in March.

The Russian economy is expected to sink into recession next year because of the sanctions and the falling price of oil, the country's main commodity.

(Reporting by Vladimir Soldatkin; Editing by Tom Heneghan)