"This was a demonstration of the ironclad U.S. commitment to our allies in South Korea, in Japan, and to the defense of the American homeland", Adm. Harry B. Harris Jr., commander U.S. Pacific Command said in a statement.

The US sent a heavy bomber over South Korea on Sunday in a show of force as North Korean leader Kim Jong-Un insisted his country's latest nuclear test was carried out in self-defence.

No significant troop movements have been detected in North Korea that could signal an imminent provocation, and the U.S.is in talks with South Korea about deploying more strategic assets to the peninsula, South Korean Defense Ministry spokesman Kim Min-seok said Monday at a briefing.

A handout picture provided by the South Korean Air Force on January 11, 2016 shows a US B-52 strategic bomber flying over South Korea with fighter jets from the two countries, over South Korea, January 10, 2016.

"After North Korea conducted a nuclear test, its military may stage unexpected provocations", Lee said when visiting the United States airbase in Osan with commander of U.S. forces in South Korea Curtis Scaparotti.

That could produce humanitarian consequences and problems on China's border with North Korea, but nothing as severe as North Korea's possession of a hydrogen bomb.

He's also set to meet with Russian officials at an unspecified date.

South Korea's president Park Geun-hye plans to make a speech to the nation on Wednesday in which she is expected to express strong will to respond to North Korea's nuclear test, a presidential official said.

Tensions have escalated since Pyongyang claimed it tested a hydrogen bomb last week, with the two Koreas continuing to blast loudspeaker propaganda along the border yesterday.

Its creation allowed South Korean companies to benefit from the low cost of North Korean labor.

The talks, to be held Wednesday in Seoul, come about a month after Ambassador Sung Kim, U.S. special representative for North Korea policy; Hwang Joon-kook, South Korea special representative for Korean Peninsula peace and security affairs; and Japanese delegate Kimihiro Ishikane met in Washington, D.C., in December.

The loudspeaker bursts risk pushing South Korea and North Korea "toward the brink of war", North Korean official Kim Ki Nam said on Friday, Yonhap reported.

North Korea's recent nuclear test has further strained its relationship with China, its key provider of economic aid and trade.

Another official reportedly said that the sound coming from North Korea was "very weak", but analysts had previously noted that Pyongyang's primary concern would be to nullify the impact of South Korea's messages north of the border. After its third test, in 2013, the Security Council took about three weeks to agree a resolution that tightened financial restrictions and cracked down on its attempts to ship and receive banned cargo.