North Korea will convene a surprise parliamentary session next month amid fears that tensions over the sinking of a South Korean warship will reignite Cold War confrontation.

The Supreme People's Assembly (SPA) will meet on June 7 in Pyongyang, the official Korean Central News Agency said on Tuesday without giving a reason.

The meeting will come just two months after parliament convened in April.

The rubber-stamp body normally meets once or twice a year to approve proposals from the ruling communist party, but any second meeting is normally held in the autumn.

"This is an extraordinary thing that happens at an extraordinary time," Professor Yang Moo-Jin of Seoul's University of North Korean Studies told AFP.

Cross-border relations have worsened since an explosion tore apart the 1,200-tonne South Korean corvette Cheonan near the disputed border on March 26 with the loss of 46 lives.

Suspicions are growing the North fired a torpedo. A multinational investigation will report Thursday and Seoul is considering how to respond if Pyongyang is found responsible.

"The SPA will probably discuss counter-measures to the South's actions, endorse future actions by the North's government agencies and come up with its own resolution," Yang said.

Leader Kim Jong-Il this month paid a visit to China apparently focused on building up economic ties between the two allies.

Yang said parliament is likely to endorse the outcome of Kim Jong-Il's visit and approve legal and institutional changes to enhance economic cooperation with China.

He said legislators would also likely amend regulations on inter-Korean business projects in the North, such as the Mount Kumgang resort and the Kaesong industrial estate.

The North has announced it is seeking a new business partner for Kumgang after the South refused to restart tours there.

Paik Hak-Soon of Seoul's Sejong Institute said the SPA was expected to pass a resolution blaming the South for raising tensions over the sinking ahead of the 10th anniversary of an inter-Korean declaration on peace and reconciliation.

The North denies responsibility for the sinking.

Inter-Korean ties have been on a downward spiral since the conservative government of Seoul President Lee Myung-Bak took office in early 2008 and linked major aid to the North's denuclearisation.

"The SPA is likely to review overall inter-Korean relations and adopt a resolution concerning the sinking," Paik said. "It is also likely to set up legal provisions to help strengthen economic links with China."

Baek Seung-Joo of the Korea Institute for Defence Analyses said Kim is likely to call for support for the grooming of his third son Jong-Un as eventual successor.

But Yang said the North would not publicly uphold the heir apparent until Kim senior dies or become incapacitated by illness, or until economic difficulties ease substantially.

He said this would not happen before 2012, the target year for the North to become a strong and prosperous socialist state.

Succession speculation has intensified since Kim, 68, suffered a stroke in August 2008.