MOSCOW (Reuters) - Russian President Vladimir Putin promised the mother of murdered opposition politician Boris Nemtsov on Saturday that everything will be done to find and punish her son's killers, the Kremlin said.

Nemtsov, 55, was shot four times in the back near the Kremlin in central Moscow on Friday and sympathisers on Saturday placed flowers at the place where he was shot.

In the telegram to Dina Eydman, mother of Nemtsov, Putin said: "Everything will be done so that the organisers and executors of this vile and cynical murder are punished."

He said Nemtsov had left a mark in Russian history, politics and public life and had always defended his point of view honestly.

A former deputy prime minister who had feared he would be murdered, Nemtsov was the most prominent opposition figure killed in Putin's 15-year rule.