North Korean leader Kim Jong-un has marked the birthday of his grandfather Kim Il-sung by visiting his mausoleum.

Kim visited the mausoleum, which also holds the body of his father Kim Jong-il, in the capital, Pyongyang, the official KCNA news agency said, according to BBC News.

The country is celebrating founding father Kim Il-sung's 101st birthday.

This comes amid the North's bellicose threats against South Korea, Japan and U.S. bases in the region.

Kim early on Monday, April 15 was at the Kumsusan mausoleum to pay "high tribute and humblest reverence" to the country's former leaders, KCNA says.

The streets of Pyongyang are adorned with flags and banners for the holiday, a red-letter day for one of the world's most powerful cults of personality.

Tensions have been high on the Korean peninsula after North Korea conducted its third underground nuclear test on February 12 that resulted in sanctions from the UN.

There is speculation that the North will use Kim Il-sung's birthday for a missile launch. At this time last year, it launched a rocket with the stated aim of putting a satellite into orbit to mark the 100th anniversary of Kim Il-sung's birth. The rocket broke up shortly after take-off.

The UN Security Council condemned the launch, which many outside the country saw the launch as an illegal test of long-range missile technology.

On Sunday U.S. Secretary of State John Kerry has called on North Korea's leaders to "come to the table in a responsible way" to end regional tensions, warning it risked further isolation if its threats continued.

He also reaffirmed the U.S. commitment to defend its allies, including Japan.

At a joint news conference with Japanese Foreign Minister Fumio Kishida, Kerry stressed that Seoul, Beijing, Tokyo and Washington had "committed to take action together" and to making the goal of denuclearization of the Korean peninsula "a reality".

Washington and Tokyo have a security alliance dating back to the 1950s, under which Washington is bound to protect Japan if it is attacked.

North Korea habitually issues fiery statements denouncing the U.S. and South Korea, but the rhetoric has grown increasingly aggressive since the UN imposed a fresh round of sanctions in March.