Russia's President Vladimir Putin says the world is engaged in a new arms race and Nato is failing to accommodate Russia's concerns.
In a nationally-televised speech, he condemned Nato's expansion and the US plan to include Poland and the Czech Republic in a missile defence shield.
"It is already clear that a new phase in the arms race is unfolding in the world," Mr Putin said.
"It is not our fault, because we did not start it," he said.
Mr Putin was speaking less than a month before Russians elect his successor.
In his speech, to the State Council - Russia's top politicians, officials and generals - he said other countries were spending far more than Russia on new weapons.
But Russia would always respond to the challenges of a new arms race by developing more hi-tech weaponry, he said.
Referring to Nato's activities in Central and Eastern Europe, Mr Putin said "there are many discussions on these, but... we have still not seen any real steps towards finding a compromise".
"In effect, we are forced to retaliate, to take corresponding decisions. Russia has, and always will have, responses to these new challenges," he said.
Russia has been using oil revenues to bolster its military
In December, Russia said it was planning naval exercises in the Mediterranean Sea and the Atlantic Ocean.
It has also resumed long-range patrols by its bomber aircraft.
The practice was suspended after the collapse of the Soviet Union and was revived last August, as part of a more assertive foreign policy pursued by President Putin.
Higher oil prices have enabled Russia to re-invest in its armed forces, but its military capabilities remain far below what they were during the Soviet era.
The BBC's World Affairs correspondent Nick Childs says Mr Putin's language will add to growing worries in the West about Russia's new assertiveness.
Our correspondent says there was a time when Moscow appeared weakened, short of money, preoccupied with domestic problems, and relatively passive in terms of foreign policy.
But he says it is clear that Mr Putin is sending a none-too-subtle message that Russia is back on the international stage.