Feb 6, 2:41 AM (ET)

By JUDITH INGRAM

MOSCOW (AP) - An explosion hit the Moscow metro during rush hour Friday morning, sending clouds of smoke through the tunnel and killing at least 22 people and wounding 30, the Emergency Situations Ministry said.

A severe fire broke out in the underground train and passengers were being evacuated from Avtozavodskaya station, which was about 300 yards from the site of the explosion, ministry spokesman Viktor Beltsov said.

Beltsov said at least 22 people were killed at 30 wounded, but he could not confirm the cause. Moscow hospitals were put on alert.

The explosion occurred in the second wagon of a train after it left the Avtozavodskaya station and headed northwest to the central Paveletskaya station, which is on Moscow's busy circle line, said Kirill Mazurin, spokesman for Moscow police, told NTV television.

Ambulances crowded the street outside the metro station entrance and paramedics, carrying stretchers or equipment in backpacks, rushed down the steps. Some passengers emerged, two with their faces spattered with blood, another with a bandaged head, others carried on gurneys.

Police immediately barricaded the two metro stations and stopped all traffic between the stations. Dozens of buses were rerouted to deal with the evacuated passengers, clogging up the already busy streets of the Russian capital.

Russian prosecutors said they could not rule out terrorism, but that it was too early to say definitively. President Vladimir Putin was immediately informed.

More than 700 people have been evacuated, the ITAR-Tass news agency reported, citing metro staff. Most Russians are dependent on public transportation, and the spacious train wagons are usually packed tight during rush hour traffic.

The Interfax and ITAR-Tass news agencies said the train wagon was badly damaged.

The Russian capital has been on alert for terrorist attacks following a series of suicide bombings that officials have blamed on Chechen rebels.

In December, a female suicide bomber blew herself up outside the National Hotel across from Moscow's Red Square, killing at least five others. Two suicide bombers blew themselves up at a Moscow rock concert in July, killing themselves and 14 other people. That was followed five days later by an aborted suicide bomb attack at a central Moscow restaurant that killed the sapper trying to defuse the bomb. The suspected attacker was arrested and is awaiting trial.

In August 2000, a bomb exploded at a crowded pedestrian underpass filled with kiosks at Pushkin Square, a popular meeting place located near a metro line. The attack was initially blamed on Chechen rebels, but some police later said that a turf battle between rival businessmen or criminal gangs could have been the motive.