U.S. President Barack Obama pledged Wednesday a "steadfast" commitment to defend Japan, including preventing nuclear attacks on his ally in the wake of North Korea's third nuclear test, the White House said.

In a telephone call, Obama and Japanese Prime Minister Shinzo Abe discussed steps to respond to the "highly provocative violation of North Korea's international obligations, a White House statement said.

U.S. Defense Secretary Leon Panetta discussed "immediate coordinated actions" with his South Korean counterpart on Wednesday, after North Korea staged a third nuclear test, a Pentagon spokesman said.

Panetta spoke with South Korea's Defense Minister Kim Kwan-Jin one day after Pyongyang triggered international outrage bay carrying out its latest nuclear detonation in defiance of U.N. Security Council resolutions.

South Korea said Wednesday it would accelerate the development of longer-range ballistic missiles that could cover the whole of North Korea in response to a third nuclear test by Pyongyang.

"We will speed up the development of ballistic missiles with a range of 800 kilometers (500 miles)," Defense Ministry spokesman Kim Min-Seok told reporters.

Chinese social media users berated authorities Wednesday for their relatively mild response to North Korea's nuclear test, with one likening Pyongyang to a "crazy dog" that had humiliated Beijing.

The hostility towards China's defiant neighbor contrasted with the official response from Beijing -- expressing "firm opposition" but reiterating calls for calm and restraint and not mentioning any reprisals or sanctions.

Britain summoned North Korea's ambassador on Wednesday after the pariah state sparked global fury with its third nuclear test, the Foreign Office said.

"I summoned North Korea's ambassador today to stress in the strongest terms the UK's condemnation of yesterday's nuclear test," Hugo Swire, a junior foreign minister, said in a statement.

World powers on the U.N. Security Council united to condemn North Korea's latest nuclear test Tuesday, and the United States led calls for tougher sanctions against the pariah state.

Pyongyang said its provocative detonation of a nuclear device at an underground site was a response to U.S. "hostility" and threatened still stronger action, defying warnings of United Nations measures.

Israel on Tuesday condemned North Korea's latest nuclear test, saying the world must send "a clear message" to Pyongyang that such activities were unacceptable, a foreign ministry spokesman said.

"Israel strongly condemns North Korea's nuclear test, and joins the international community in expressing the grave danger that this act poses to regional stability and international peace and security," Yigal Palmor said in a statement.

U.S. intelligence agencies believe North Korea "probably" conducted an underground nuclear test with a yield of several kilotons, the office of the Director of National Intelligence said Tuesday.

"The explosion yield was approximately several kilotons. Analysis of the event continues," the office said in a statement, confirming the blast had taken place in the area of North Korea's Punggye-ri nuclear test site.

Sanctions-hit Iran on Tuesday called for the destruction of all atomic weapons in the world after North Korea announced that it had staged its most powerful nuclear test yet.

"We need to come to the point where no country has any nuclear weapons and at the same time all weapons of mass destruction and nuclear arms need to be destroyed," foreign ministry spokesman Ramin Mehmanparast said when asked for a response to Pyongyang's claim to have detonated a "miniaturized" device.

U.N. leader Ban Ki-moon condemned Tuesday North Korea's nuclear test as "deeply destabilizing" and U.S. President Barack Obama called for swift and credible international action.

Ban condemned the nuclear weapons test as a "deeply destabilizing" provocation, his spokesman said Tuesday.