Moscow is throwing out nine Polish diplomats in retaliation for Poland's expulsion of nine Russians accused of spying.

A terse foreign ministry statement said the Poles had been given a week to leave Russia for pursuing "activities inconsistent with their status", a phrase generally used for spying.

The tit-for-tat move had been expected after Moscow made clear its fury at Poland's expulsion of nine Russian diplomats on Thursday.

Poland said they had been engaged in spying, mainly in the political and economic spheres.

But Russia said the move was an "unprecedented step" which would sour bilateral relations.

Outrageous

Sergei Prikhodko, foreign policy adviser to acting President Vladimir Putin, called Poland's decision "an outrageous action", but said it was not totally unexpected.

"Recently we have heard unfriendly statements made by top Polish officials,'' he added.

''At the same time, these same officials were trying to arrange a summit meeting between our nations' leaders. This is most unusual duplicity."

Tough measures

Earlier on Friday, Russian Foreign Minister Igor Ivanov promised "tough and adequate measures" against Poland.

"I don't know who made this decision. Was it taken by Warsaw or under someone's orders?" he asked.

Russian intelligence sources suggested Poland had acted under the influence of the West, which wanted to "test" acting President Vladimir Putin.

"[The Poles] would never have taken these actions on their own," Interfax quoted the sources as saying.

"If [Western powers] want to test Putin then they will see. But it is the Poles who will pay the price.''

Nato

Poland, a former member of the Soviet-led Warsaw Pact, joined the Nato military alliance last March in a move staunchly opposed by Russia.

But Polish Foreign Ministry spokesman Pawel Dobrowolsky strongly denied any outside interference in its decision to expel the nine Russians.

Polish Government spokesman Krzysztof Luft said the counter-intelligence agency "investigated and provided evidence of active espionage activities against Poland's interest in 1999 by a group of Russian diplomats".

Konstanty Miodowicz, who sits on the parliament's secret service committee, was quoted as saying the Russians used "aggressive operational resources" to gather classified information illegally.

Arrests

The Russian Embassy, among the biggest in Warsaw, has about 60 diplomats.

Poland has about 40 diplomats in Moscow and another dozen split between consulates in St Petersburg and the Baltic enclave of Kaliningrad.

Last year, Polish counter-intelligence arrested three army officers on charges of spying for Russia in the early 1990s.

Poland last expelled a Russian diplomat for spying in 1993.