1MDB highly politicised by certain people for own political benefit - Najib

He said they had been "feeding foreign authorities with at times, false or incomplete information."

"Those outside Malaysia cannot always appreciate these complexities, but it is something they should bear in mind to avoid becoming entangled in what has become a domestic political matter," he said in a written interview with Nikkei Asian Review ahead of his three-day official visit to Japan, beginning today.

The visit is at the invitation of his Japanese counterpart, Shinzo Abe.

Najib said Malaysian authorities had actually led the way in investigations into 1MDB, and it was he himself who first instructed multiple authorities in Malaysia to conduct investigations.

"For example, the company has been the subject of investigations by the Malaysian Anti-Corruption Commission, the auditor-general, the police and the bipartisan parliamentary Public Accounts Committee, which includes Opposition politicians," he said.

Najib was asked about foreign governments investigating misappropriation of funds related to 1MDB, whether he considered this to be interference and if Malaysia would reopen its own probe.

The prime minister said that he had always made it clear that full cooperation should be extended to any investigation provided it was in accordance with the laws of Malaysia.

"Furthermore, as I have consistently stated, if any wrongdoing is proven, the law will be enforced without exception," he added.

On Malaysia's stance on The Hague's ruling on the maritime claims by China, Najib said Malaysia had consistently held, and expressed, the view that all claims in the South China Sea must be based and resolved in accordance with international law.

"We believe it is important for all parties to respect diplomatic and legal processes, and resolve any disputes and differences peacefully through negotiations," he said.

On whether ASEAN's consensus-based process be changed to one based on a majority for quicker decision-making, Najib said this was unique and it was the ASEAN way, and it should be preserved.

"Everything that ASEAN has achieved is as a result of the collective efforts of its 10 member states. As such, this consensus style of decision making has served the community well -- politically, economically, socially and culturally -- and should be preserved."

On his visit to Japan, Najib said he and Abe would be discussing bilateral matters and issues of regional and international importance.

He will also meet with ministers in charge of various departments including land, infrastructure, transport and tourism and the business community.

Najib said Malaysia and Japan are in the second phase of the Look East Policy, and "in line with that, we will continue to enhance institutional cooperation between our two countries".

"In particular, I am committed to increasing trade and investment flows - specifically in areas such as innovation and cutting-edge technology, high-tech skills and services development, and renewable energy."