STOCKHOLM - Russian Prime Minister Vladimir Putin expressed worries again on Wednesday about the expansion of NATO, which has already taken in former Soviet states as members.

"The expansion of NATO infrastructure towards our borders is causing us concern," Putin told a news conference after meeting Swedish Prime Minister Fredrik Reinfeldt.

"NATO is not simply a political bloc, it is a military bloc. No one cancelled the agreements on how the bloc reacts to external threats. It is a defence structure," added Putin.

NATO has already taken in the three former Soviet Baltic states as members, as well as old Warsaw Pact nations including Poland and the Czech Republic.

Moscow has long been worried by the military alliance's growth and the possibility of its further expansion to take in former Soviet republics such as Georgia or Ukraine. And it is wary of US and NATO plans for a European missile defence shield, which it fears could be a threat to its security unless Russia too is integrated into such a system.

Visiting Denmark on Tuesday, Putin critised the Western coalition attacking Libya, saying it had neither the right nor the mandate to kill the country's leader, Muammar Gaddafi.

Sweden is taking part in the NATO operation in Libya, though it is not a member of the military alliance.

In the context of the Libya operation, Putin also said decisions on using military force were being taken too easily.

He contrasted this with the Soviet war in Afghanistan in the 1980s, when he said Soviet commanders were much more careful in their use of force for fear of causing civilian deaths and casualties.