President Barack Obama has warned North Korea that it faces being further isolated after the reclusive state's launch of a long-range rocket ended in failure.
The White House has suspended a deal for significant food aid to the country after the incident, which Pyongyang denied was a missile test in disguise.
North Korea said it had planned to put a weather satellite into orbit. Its scientists were said to be trying to work out what had caused the rocket to explode over the Yellow Sea.
Mr Obama said he was deeply concerned by the launch, which violated UN Security Council resolutions, adding that "they've been trying to launch missiles like this for over a decade now and they don't seem to be real good at it".
He added: "We will continue to keep the pressure on them and they'll continue to isolate themselves until they take a different path."
US Ambassador to the UN Susan Rice, the current UN Security Council president, has refused to speculate on any sanctions against North Korea.
But the launch was widely condemned by the international community, including the UK and Japan, and UN chief Ban Ki-Moon described the move as "deplorable". Russia had urged North Korea to refrain from the launch.
Some 200 foreign journalists had been invited to the capital for weekend-long celebrations, which included a mass ceremony on Friday, after the launch.
It was attended by new leader Kim Jong-Un, who was seen waving at tens of thousands of people to honour two large statues of predecessors Kim Il-Sung and Kim Jong-Il.
A US official warned that Pyongyang faced additional sanctions if it defied the international community again.
White House National Security Council spokesman Ben Rhodes said: "If they continue to take additional provocative actions, we of course have to continue to look at ways in which we could tighten sanctions on the North Koreans, and take additional steps to apply pressure on the regime."