In pictures: Moscow station blast

1 of 6 An explosion hits a street near the busy Rizhskaya metro station, at the end of Moscow's evening rush-hour.

2 of 6 A number of people are killed and many more are injured by the blast, thought to have been a deliberate attack.

3 of 6 One report says the bomb was packed with metal fragments.

4 of 6 Moscow has the world's busiest subway system, and the station is on one of the most used routes north of the city.

5 of 6 Russian police raised the possibility that the explosion was caused by a female suicide bomber.

6 of 6 They are also working on the theory that the blast was caused by a car bomb.