MOSCOW, Feb 13 (Reuters) - The United States has told its citizens to leave Russia immediately due to the war in Ukraine and the risk of arbitrary arrest or harassment by Russian law enforcement agencies.

"U.S. citizens residing or travelling in Russia should depart immediately," the U.S. embassy in Moscow said. "Exercise increased caution due to the risk of wrongful detentions."

"Do not travel to Russia," the embassy said.

The United States has repeatedly warned its citizens to leave Russia. The last such public warning was in September after President Vladimir Putin ordered a partial mobilisation.

"Russian security services have arrested U.S. citizens on spurious charges, singled out U.S. citizens in Russia for detention and harassment, denied them fair and transparent treatment, and convicted them in secret trials or without presenting credible evidence," the embassy said.

"Russian authorities arbitrarily enforce local laws against U.S. citizen religious workers and have opened questionable criminal investigations against U.S. citizens engaged in religious activity."

Russia has opened a criminal case against a United States citizen on suspicion of espionage, the Federal Security Service(FSB) said in January.