The United States said it aims to maintain good ties with all Southeast Asian countries including Malaysia, regardless of the US Department of Justice's (DOJ) 1MDB-linked lawsuits.

Asked if the suits will sour ties with the Najib Abdul Razak administration, US deputy assistant secretary Walter Douglas said he had cordial meetings with Malaysian officials during his trip to Kuala Lumpur on Sept 8.

"We want a warm relationship with all countries in Southeast Asia, of all countries of Asia.

"That's the most important thing, to have a good relationship," he said when met on the sidelines of the East-West Centre International Media Conference in New Delhi, India on Friday.

Douglas is deputy assistant secretary of state for public affairs, public diplomacy and regional and security policy of US State Department's East Asia and Pacific Affairs bureau.

Najib this week uploaded to Facebook a picture of him shaking hands with US President Barack Obama at the East Asia Summit in Laos, indicating good rapport with the global superpower.

This in spite his stepson Riza Aziz and their family friend, Malaysian businessman Jho Low being among four named in the DOJ civil forfeiture action to seize over US$1 billion in assets allegedly purchased in the US with funds said to be siphoned from 1MDB.

The Malaysian duo and two former United Arab Emirate state firm officials Khadem al-Qubaisi and Mohamed Badawy al-Hussainy will have to respond to the lawsuits this month, the DOJ said.

The DOJ also alleged US$731 million of funds originating from 1MDB entered the bank accounts of an unnamed 'Malaysian Official 1'.

Minister in the Prime Minister's Office Abdul Rahman Dahlan has eventually admitted 'Malaysian Official 1' is Najib, but pointed out the prime minister was not named and said this meant he is not subject of what the DOJ calls its biggest anti-kleptocracy action to date.

Najib has consistently denied abusing public funds.

'Act against North Korea'

On a separate matter, Douglas urged all countries with diplomatic ties with North Korea to act in the face of the hermit nation's nuclear test yesterday.

Malaysia is among the handful of countries that have diplomatic ties with North Korea, with Malaysian travellers able to visit the nation visa-free.

"The North Korea test is troubling ... those with diplomatic relationships with North Korea should do something to stop that," he said at the conference.

US Foreign Secretary John Kerry in a statement later said the test is "unlawful, flagrantly violating multiple UN Security Council resolutions and DPRK (North Korea)'s own commitments".

"The DPRK's repeated and willful violations of its obligations under UN Security Council resolutions, its belligerent and erratic threats, and web of illicit activities around the world indicate it has no interest in participating in global affairs as a responsible member of the international community," he said.

Wisma Putra has not commented on the latest test but condemned North Korea's nuclear test in January.

Malaysia and Singapore are the only two countries that presently have no visa requirement for a 30 day visit to North Korea, according to IATA's website.