North Korea held a brief live-fire drill near its maritime border with South Korea on Tuesday, hours after U.S. President Barack Obama wrapped up an Asia trip that Pyongyang had denounced as provocative.

A similar drill one month ago saw a number of shells land on the South Korean side of the border, prompting a response that resulted in both countries firing hundreds of artillery rounds into each others territorial waters.

Pyongyang launched a vicious personal attack on South Korean President Park Geun-Hye Sunday, calling her a "prostitute" in thrall to her "pimp" Barack Obama, as it said it was ready for "full-scale nuclear war".

In a diatribe that was strongly worded even by the standards of its normally florid prose, the North lashed out at the relationship between a "master and its puppet" and threatened Park would pay a "dear price".

North Korean leader Kim Jong-Un has carried out a rash of visits to military installations and chaired a meeting of senior figures in the armed forces, state media said Sunday, amid global unease over a possible nuclear test.

The announcement by the Korean Central News Agency (KCNA) comes the day after U.S. President Barack Obama lambasted the North as a "pariah" and said any atomic blast would lead to "more isolation".

A North Korean nuclear test within days "cannot be ruled out" analysts said Saturday, after new satellite imagery showed heightened activity at the test site.

The report by the Institute for Science and International Security (ISIS) chimes with other findings and suggests Pyongyang is moving towards an underground detonation.

North Korea is a "pariah state" whose heavily militarized border with the South marks "freedom's frontier", U.S. President Barack Obama told American troops in Seoul on Saturday.

Obama, who was wrapping up a two day visit to South Korea, said Pyongyang's continued pursuit of nuclear weapons is "a path that leads only to more isolation".

North Korea said Friday it had been holding a 24-year-old U.S. tourist in custody for more than two weeks after he apparently ripped up his visa at immigration and demanded asylum.

The announcement, made in a brief dispatch carried by the North's official KCNA news agency, came as U.S. President Barack Obama wrapped up the first part of a two-day visit to South Korea.

North Korea will gain "nothing" by making threats, U.S. President Barack Obama said Friday, warning it of sanctions with "more bite" if it went ahead with a fourth nuclear test.

Speaking in South Korea as satellite images revealed the North could be preparing for an underground explosion, Obama stressed that Washington and Seoul stood "shoulder to shoulder" in their refusal to accept a nuclear North Korea.

Five years after refashioning U.S. foreign policy to emphasize Asia, President Barack Obama will face questions over his strategy's content and staying power in the region this week.

Obama will counter the impression that events, including carnage in Syria and the East-West showdown over Ukraine have dragged his administration’s attention elsewhere.

New satellite imagery suggests North Korea is preparing to conduct its fourth nuclear test, a U.S. think-tank said Friday just hours before President Barack Obama arrives in South Korea for a visit.

The analysis by the U.S.-Korea Institute at Johns Hopkins University echoed recent warnings from South Korea that the North might be planning a test to coincide with Obama's two-day visit.

North Korea has apparently sealed a tunnel at its nuclear test site, a government official said Thursday ahead of U.S. President Barack Obama's arrival in Seoul for a two-day visit.

South Korea's defense ministry warned earlier this week that the North could be preparing to carry out a fourth nuclear test, citing increased activity at the Punggye-ri site.