He said North Korea has tested the limits of patient diplomacy intended to persuade the reclusive communist country to accept international demands and end to its nuclear program.
"Diplomacy has to involve the other side engaging in serious way, and we have not seen that reaction from North Korea," Obama said. "I don't think there should be an assumption that we will simply continue down a path in which North Korea is constantly destabilizing the region and we continue to act in the same ways."
Obama said North Korea's recent nuclear test and missile launches were provocative. He noted that Russia and China have been more engaged on the matter than in the past, indicating that those countries, too, recognize the possible peril.
Obama spoke after a private meeting with French President Nicolas Sarkozy in this Normandy city before the leaders commemorated the D-Day invasion that cemented the trans-Atlantic alliance.
"This day marks not only the triumph of freedom but it also marks how the trans-Atlantic alliance has allowed for extraordinary prosperity and security on both sides of the Atlantic," Obama said.
On other matters of international importance, Sarkozy agreed with Obama's efforts to bring about a Mideast peace that provides for separate Israeli and Palestinian states, and on the need to thwart Iran's disputed nuclear ambitions.
"We want peace. We want dialogue. We want to help them develop. But we do not want military nuclear weapons to spread and we are clear on that," said Sarkozy, who met Wednesday with Iranian Foreign Minister Manouchehr Mottaki. "I said to him ... that he had to take this hand stretched out by Barack Obama."
Obama reaffirmed that there must be "tough diplomacy" with Tehran and said Iran's actions are contrary to its leaders' insistence that the country does not seek nuclear weapons.
He said he wants to see greater U.S.-Russian efforts to limit nuclear weapons and said that his work against nuclear proliferation and the efforts toward that end by other countries should signal Iran's leaders that they are not being singled out for rebuke.
Sarkozy said his country would take some detainees from the U.S. prison at Guantanamo Bay, Cuba, as the Obama administration has asked.
Obama said he and Sarkozy will work "in close collaboration" on many issues, including anti-terrorism strategy.
He also said the United States has authorized all of the government's resources to investigate an Air France plane that disappeared off the coast of South America.
Investigators are searching for debris from Air France Flight 447, which lost contact with officials on June 1 during a flight from Rio de Janeiro to Paris. Two Americans were aboard the 228-person flight.