The radio said a public building was damaged in the north of Tehran but that no-one was hurt.

It also reported that an unnamed armed group had tried to attack a third building - the headquarters of the Revolutionary Guard - but ran away, leaving behind explosives.

Opposition claim

The Iraq-based opposition group, the Mujadehin Khalq, issued a statement saying it was responsible for the first blast, in reprisal for the killing of a number of its fighters in clashes with government forces in western Iran late last year.

The authorities have urged the public to attend the funerals of those who died as a sign of protest.

Correspondents say there may be a connection between the explosions and the anniversary on Thursday of the death of the founder of the Islamic Revolution, Ayatollah Khomeini.

Reformist President Khatami

In the 1980s, the Mujahideen were behind a series of huge explosions which killed a number of senior Iranian leaders. But a ruthless crackdown reduced their ability to operate. More recently their credibility inside Iran has been eroded by their close association with the Iraqis.

The BBC correspondent in Iran says that because the Mujahideen have not bombed the Iranian capital for some time, this might signal a change in tactics.

In recent months, Iran has been at the centre of an intensifying power struggle between the moderate reformists supporting President Mohammad Khatami and hard-line conservatives who oppose his social and political reforms.