The Democratic People's Republic of Korea (DPRK) has sent jet fighters to test the South's air defenses and threatened to reduce the Republic of Korea (ROK) to ashes as it tries to push the new government in Seoul to back off from its hard line with Pyongyang.

Monday, the ROK's biggest daily newspaper said the DPRK's jets had flown sorties close to the ROK airspace at least 10 times since Lee Myung-bak became president on Feb 25. At the weekend the North said it was ready to attack.

Lee's government has criticized Pyongyang on human rights and nuclear issues.

Last week Pyongyang expelled ROK officials from a joint factory park just north of the heavily armed border once hailed as a model of economic cooperation.

It then test-fired missiles into the Yellow Sea, following that up at the weekend with a threat to launch a pre-emptive strike to "not merely plunge everything into flames, but reduce it (the South) to ashes".

It has also threatened to attack ROK naval vessels patrolling in disputed Yellow Sea waters, suspend inter-Korean dialogue and stop taking apart its nuclear weapons plant as called for under an international deal.

Analysts say the North could next cut inter-Korean projects, slow down or shut the joint factory park in Kaesong and come up with a new set of military moves.

The DPRK moves come as conservatives are trying to win control of the South's parliament from left-of-center forces in an April 9 election. If conservatives win a majority, it would significantly strengthen Lee's hand during his five-year term.

Analysts said the North's influence in ROK politics has waned over the years and they see the recent turmoil as having no major impact in the election.