VOTKINSK, Russia - Russian Prime Minister Vladimir Putin on Monday likened the UN Security Council resolution supporting military action in Libya to medieval calls for crusades.

In some of his harshest criticism of the United States since President Barack Obama began a campaign to improve ties, Putin also compared the intervention with the Bush-era invasion of Iraq and said it showed Russia is right to boost its military.

Putin, whose country opted not to block the UN resolution last week leading to the strikes, said that Muammar Gaddafi's government was undemocratic but emphasised that did not justify military intervention.

"The resolution is defective and flawed. It allows everything," Putin told workers at a Russian ballistic missile factory. "It resembles medieval calls for crusades."

Russia, a veto-wielding permanent UN Security Council member, abstained from the vote on Thursday in which the council authorised a no-fly zone over Libya and "all necessary measures" to protect civilians against Gaddafi's forces.

"What troubles me is not the fact of military intervention itself -- I am concerned by the ease with which decisions to use force are taken in international affairs."

"This is becoming a persistent tendency in US policy," Putin said.

"During the Clinton era they bombed Belgrade, Bush sent forces into Afghanistan, then under an invented, false pretext they sent forces into Iraq, liquidated the entire Iraqi leadership -- even children in Saddam Hussein's family died."

"Now it is Libya's turn, under the pretext of protecting the peaceful population," Putin said. "But in bomb strikes it is precisely the civilian population that gets killed. Where is the logic and the conscience?"

CASE FOR DEFENCE

Putin said that "today's events, including in Libya, confirmed our decisions on strengthening Russia's defence capabilities were correct."

Russia is planning to spend nearly 20 trillion roubles ($707.2 billion) through 2020 to modernise its armed forces.

Russia, which faces accusations of backsliding on democracy during Putin's 2000-2008 presidency, has repeatedly opposed international intervention in what it says are nations' internal affairs.

"The Libyan regime does not meet any of the criteria of a democratic state but that does not mean that someone is allowed to interfere in internal political conflicts to defend one of the sides," Putin said.

Russian-U.S. relations have improved in the past two years under Obama's "reset", capped by the New START nuclear arms reduction treaty that took effect last month.