North Korea has dismissed a claim by a right-wing US website that it might have been behind the deadly bombings in Boston, decrying the report as "false propaganda" and insisting that it is against all terrorism.

"When the (North) feels necessary to strike the US, it would not resort to such heinous terrorism in hiding," Pyongyang's Korean Central News Agency (KCNA) said.

WorldNetDaily (WND), a controversial US website that carries news and commentary from a conservative viewpoint, published Wednesday an article claiming North Korea might be involved in Monday's attack that left three dead and 180 injured.

"The Boston Marathon bombing...(raised) questions among analysts whether Pyongyang, as in some of its past terrorism, used proxies to carry out the attack," it said, amid ongoing tensions between North Korea and the United States.

The website also claimed the nation had "a history of a relationship" with Al-Qaeda, which teaches in its online magazine how to make the type of pressure-cooker bomb used in the Boston attacks.

The WND report came before Boston police caught up with two brothers of Chechen origin who are suspected of carrying out the marathon attack. One was killed in a shootout and the other remains in hospital after he was apprehended late Friday.

The North's Korean Central News Agency, in an editorial published late Saturday, slammed the WND claim as "false propaganda which does not deserve even a passing note".

It denied any links between Pyongyang and Al-Qaeda, and accused the conservative website of cooking up "sinister plots" to tarnish North Korea's image.

"The (North) would like to stress once again that it has no touch with Al-Qaeda and has consistently maintained the stand of opposing all forms of terrorism," the English-language editorial said.

North Korea has for weeks been issuing threats of missile strikes and nuclear war against South Korea and the United States, angered by fresh UN sanctions imposed for its latest nuclear test and by joint South Korea-US military exercises.