Warsaw:
US President Barack Obama told European allies on Tuesday they had a responsibility to boost defence spending in return for US protection amid new instability in Europe.
"We have seen a steady decline, that has to change," Obama said, bemoaning cuts in military spending across Europe in an age of economic austerity.
Obama said that with a few exceptions, including Poland, European nations had not been pulling their weight in the alliance - a fact that was exposed by the East-West showdown over Ukraine.
"They expect full membership when it comes to their defence, that means they have also got to make a contribution that is commensurate with full membership," Obama said at a press conference in Warsaw.
Obama said the NATO alliance was the "cornerstone" of US security.
"But we can't do it alone," he said.
"We have to make sure everybody who is a full member of NATO has full membership."
Obama spoke at a press conference with Polish President Bronislaw Komorowski who announced that in recognition of the new security environment following Russia's annexation of Crimea, his government would boost defence spending to 2.0 percent of GDP.