The half-brother of North Korea's leader Kim Jong-Un was poisoned with the lethal nerve agent VX in a brazen Cold War-style assassination on February 13 in Kuala Lumpur International Airport.

His comments Sunday came as North Korean state media reported on Pyongyang testing a powerful new rocket engine, in an event apparently timed to coincide with the visit of US Secretary of State Rex Tillerson to Beijing over the weekend.

A North Korean military unit tasked with striking USA bases in Japan was involved in those launches, the state news agency said. They have been "playing" the United States for years. A Vietnamese woman and an Indonesian woman have already been charged in the case. Interpol has issued an worldwide arrest warrant for the four men.

One of the sources said, "There could be a few more people assisting (in the murder), which will raise the number of the total of North Koreans involved to around 10".

"Obviously we have a very bad relationship with them, we're not pals, [but] to be able to exert influence on North to encourage our friends in the region who I think are rightfully concerned with North Korea as well to step up".

They are demanding possession of his body and an independent investigation by an global organization.

In a stop in Seoul on Friday, Tillerson said that "all options are on the table" for dealing with North Korea and that, while the United States did not want a military confrontation, it would resort to military actions if necessary. Malaysia in turned described the North Korean envoy as "delusional". The two countries have made a decision to expel ambassadors while scrapping visa-free travels for each other's citizens. We are investigating a murder that took place in our jurisdiction.

"So, it is our responsibility to investigate in a transparent manner and in accordance with existing laws", he added.

"We will not allow the Malaysian Ex-Policemen Association to collect any form of donations from the public because now, the public can contribute to this special fund which is chaired by Deputy Prime Minister Datuk Seri Dr Ahmad Zahid Hamidi", he added.