'No rewards'

"We are going to take a very hard look at how we move forward on these issues," Obama said after a meeting Nicolas Sarkozy, the French president, the city of Caen in Normandy, northern France.

"I don't think that there should be an assumption that we will simply continue down a path in which North Korea is constantly destabilising the region and we just react in the same ways.

"They have made no bones about the fact that they are testing nuclear weapons, testing missiles that would potentially have intercontinental capacity.

"We are not intending to continue a policy of rewarding provocation."

North Korea last launched a long-range missile in April. It has since carried out a nuclear test and several short-range missile tests. 

North Korea is believed to be preparing for a further long-range missile test.

Obama said that the UN security council was preparing a new resolution on North Korea.

He asserted that China and Russia - the two major powers closest to Pyongyang - were also taking a stricter stance.

"They understand how destabilising North Korea's actions are," he said.

Obama was talking ahead of a ceremony to mark the 65th anniversary of the D-Day landings, a key date for the allies' victory in the second world war.