Obama: North Korea nuclear program poses "grave threat"

WASHINGTON (Reuters) - U.S. President Barack Obama said on Tuesday that North Korea's nuclear and missile programs posed a grave threat to the region and to the world and called for a sustained effort to enforce international sanctions.

Obama was speaking at a news conference after meeting South Korean President Lee Myung-bak at the White House. North Korea said at the weekend it would start a uranium enrichment program and weaponize all its uranium in response to new U.N. sanctions.