WASHINGTON - US President Barack Obama on Wednesday reaffirmed his country's commitments to Japan's security, including defending Japan with US nuclear umbrella.

Obama called Japanese Prime Minister Shinzo Abe by phone over a fresh nuclear test by the Democratic People's Republic of Korea and they discussed steps to respond to this "highly provocative violation" of DPRK's international obligations, the White House said in a statement.

"President Obama reaffirmed that the United States remains steadfast in its defense commitments to Japan, including the extended deterrence offered by the US nuclear umbrella," the statement said.

Pyongyang, despite strong opposition from the international community, conducted its third nuclear test Tuesday, drawing condemnation from the UN Security Council and a number of countries.

The DPRK's official KCNA news agency, however, said the test was part of the country's "practical measures of counteraction" to defend its security and sovereignty against hostile US policies that have violated the DPRK's "rights to launch satellite for peaceful purposes."

Obama and Abe also "pledged to work closely together to seek significant action at the United Nations Security Council and to cooperate on measures aimed at impeding North Korea's nuclear and ballistic missile programs," the statement said.

Obama said he looked forward to "in-depth discussions" with Abe when he visits Washington later this month, according to the statement.

On Tuesday, Obama made similar pledge to the Republic of Korea when he called President Lee Myung-bak following the DPRK's third nuclear test.

The DPRK conducted two previous nuclear tests in 2006 and 2009 respectively.