LONDON (Reuters) - Russia's defence ministry said on Friday that Ukrainian fighters and foreign mercenaries had been "securely blockaded" at the Azovstal steel plant where they have been holding out in the Ukrainian city of Mariupol.

       President Vladimir Putin had ordered his defence minister on Thursday to block off the vast Azovstal complex "so not even a fly can get through" rather than try to storm it.

       The defence ministry also said Russia had hit dozens of targets in the Donetsk and Kharkiv regions of Ukraine on Friday.

       In a statement, the ministry referred to the remaining fighters of Ukraine's Azov battalion, holed up in the steel plant, as Nazis.

       "All remnants of the Ukrainian 'Azov' Nazis, together with foreign mercenaries from the United States and European countries, are securely blockaded on the territory of the Azovstal plant," it said.

       "The Nazis are ignoring our demands to release the women and children allegedly with them to travel freely in any direction."

       Putin invaded Ukraine on Feb. 24 with the stated aim of demilitarising and "denazifying" the country, which Kyiv and the West have rejected as baseless war propaganda.

       The defence ministry said the situation in Mariupol, a city which had been reduced to ruins in the worst devastation of the eight-week war, had "returned to normal" and humanitarian aid was being delivered.

       Ukraine estimates tens of thousands of civilians have died in Mariupol, once home to 400,000 people. The United Nations and Red Cross say the civilian toll is at least in the thousands.

       (Reporting by Reuters)