Russia has said it will expel two Swedish diplomats in a tit-for-tat move following Sweden's expulsion of two Russian diplomats last month.

The Russian Foreign Ministry said two diplomats had been declared persona non grata for "activities damaging to the interests of Russian state security".

They have taken this decision which we consider groundless

Sven Hirdman Swedish Ambassador

The Russian diplomats were expelled from Sweden over alleged espionage at telecoms and defence giant Ericsson.

At the time, Russia said it reserved the right to make a "commensurate" response.

It is not clear when the deadline for the two Swedish officials to leave the country is or whether they have already left. Their identity has not been released.

The expulsion drew accusations from Stockholm that Russia was returning to Soviet-era foreign policy tactics.

"It is sad that Russia is resorting to this kind of outdated foreign policy," Swedish Foreign Minister Anna Lindh told Swedish radio, adding there were no grounds for Moscow's action.

"When we declare people persona non grata in Sweden, it is because they have done something that is not allowed in Sweden."

Ms Lindh said Sweden did not plan to take any further measures against Moscow.

'Espionage'

Last month, Swedish police arrested three people on suspicion of supplying confidential company documents to Russia in an alleged industrial espionage plot at an Ericsson subsidiary.

Although best known for its mobile and office phones, Ericsson is a major manufacturer of radar and missile-guidance technology for the Gripen fighter jet, Sweden's main strike warplane.

About 2,000 of Ericsson's 72,000 employees work in the group's defence operations.

Ericsson has not said what documents were leaked, although a senior source said they did not appear to be linked to any military projects, Reuters news agency reports.

The Swedish media have speculated that the classified documents could concern radio equipment or perhaps radar systems, such as those manufactured by Ericsson for the Anglo-Swedish JAS-39 Gripen jet fighter, or technology that controls telephone networks.