US Director of National Intelligence James Clapper announced on Tuesday that North Korea has restarted a plutonium reactor that could provide fuel for nuclear weapons.
"We further assess that North Korea has been operating the reactor long enough so that it could begin to recover plutonium from the reactor's spent fuel within a matter of weeks to months," he said.
Obama, Park, Abe agree on tough sanctions for North Korea
After North Korea launched its long-range rocket, the United States President Barack Obama spoke with the leaders of South Korea and Japan and reassured them of US support, the White House said on Tuesday.
Obama had a telephone conversation with both leaders separately on Monday night and they agreed on the need for a "strong and united international response to North Korea's provocations, including through a robust UN Security Council Resolution," the White House added
The US military also stated it wants to set up a sophisticated missile defence system in South Korea as quickly as possible.
North Korea fired a long-range rocket earlier on Sunday despite United Nations sanctions banning it from having ballistic missile technology.
The plan creates distress, as it could improve Pyongyang's long-range missile technology. North Korea previously had also said that it tested a hydrogen bomb on Jan. 6.
After the incident, UN Security Council condemned North Koreas long-range rocket launch and vowed impose "serious consequences" on the country.
The United Nations Security Council had previously banned North Korea from conducting tests that use ballistic missile technology, and is also under heavy sanctions, due to its ongoing nuclear and ballistic missile programmes.