the luxury GUM shopping centre near the Kremlin. In the capital alone, more than 50,000 people were caught up in the alerts, reports said.

image caption Muscovites milled around outside the GUM centre after it was evacuated

Pro-Kremlin newspapers have pointed to a "major hacking attack", possibly from Ukraine. State TV said 205 companies and organisations had been targeted nationally.

Other reports suggested the threats were made via scrambled internet connections and were difficult to source. One official was quoted as saying the evacuations were part of an anti-terrorist drill but that has not been confirmed.

Four days of threats

The hoax calls began on Sunday but the extent of the alerts only became clear by Tuesday:

In Chelyabinsk, in the southern Ural mountains, more than 11,000 people were cleared from 10 buildings onTuesday

In Perm to the north-west, 5,700 people had to leave schools and public buildings

In the southern city of Stavropol alone, 1,500 phone hoaxes had been received, state TV reported

Other cities affected ranged from Krasnoyarsk, Novosibirsk and Omsk in Siberia to the enclave of Kaliningrad in the far west

image copyright AFP image caption Police searches continued in cities across Russia (file pic)

They continued to spread on Wednesday, with airports also targeted:

In Moscow, bomb alerts were reported in Red Square, at railway stations, universities and shopping centres

The River Volga cities of Samara and Saratov were hit, with seven shopping centres targeted in Saratov alone

Several more Siberian cities were affected: in Ulan-Ude there were alerts at six shopping centres, four schools and bus and railway stations

Irkutsk and Yakutsk were hit, and