Russian President Vladimir Putin says NATO's continued enlargement creates the impression that the alliance is trying to replace the United Nations.
He made his remarks on Saturday at a joint press conference in Moscow with German Chancellor Angela Merkel who is visiting Russia.
Ms. Merkel sad NATO is purely a defensive alliance.
The German leader also met with President-elect Dmitri Medvedev who is to be inaugurated in May. She is the first Western head of state to meet Mr. Medvedev since he was elected on March 2.
President Putin warned that his successor will defend Russia's interests as staunchly as he has and that Russia's partners should not expect to find him any easier.
Germany and Russia have disagreed over a range of issues in recent years, including Kosovo's independence, Iran's nuclear program and Russia's energy policy.
Russia briefly stopped natural gas supplies to Ukraine on Wednesday, which in turn interrupted delivery to other European markets. Germany gets most of its natural gas supplies from Russia.
The German chancellor has criticized Russia's human-rights and media-freedom record. She has also questioned the fairness of Russia's presidential election.
President Putin has opposed a possible admission of former Soviet republics Ukraine and Georgia to NATO, saying that many people in those countries are against joining the Western alliance. He has also disagreed with Germany over U.S. plans to deploy a missile defense system in Poland and the Czech Republic.
Some information for this report provided by AFP and Reuters.