BANGKOK - The United States should engage in direct diplomacy with Pyongyang alongside sanctions imposed over its nuclear and ballistic missile programmes, said the chief US negotiator for North Korea on Friday (Dec 15).

"We should exercise direct diplomacy as well as sanctions. That is our policy, which is based on pressure and engagement, and we do want to engage in pressure and diplomacy," Mr Joseph Yun, the American special representative on North Korea, told reporters in Bangkok on Friday.

He said the US was open for dialogue with North Korea, but said the "first credible step" in lowering tensions should come in the form of Pyongyang halting provocations like launching missiles.

"I hope we get the chance to address the whole question through diplomacy," said Mr Yun, a veteran Asia hand at the State Department.

US President Donald Trump has said that all options, including military options, are on the table in dealing with Pyongyang. The isolated state defied UN sanctions on Nov 29 to test its most powerful missile yet, which it claimed could strike anywhere in the US.

In response, the US ambassador to the UN Nikki Haley said North Korea's regime will be "utterly destroyed" if war breaks out. She also urged the world to cut all ties with Pyongyang.

Mr Yun was visiting Bangkok as part of tour through Asia - including Japan - to muster regional support for pressure on Pyongyang.

On Thursday (Dec 14), he had what he called "constructive, open-ended" talks with Thailand's Deputy Foreign Minister Virasakdi Futrakul as well as National Security Council chief Wanlop Rugsanoh.

Mr Yun stressed the US has no particular concerns about Thailand, which says it has substantially cut trade with North Korea.

Thailand was the fourth-largest trade partner, after China, Russia and India.

According to the United Nations trade database, Thailand exported US$46.8 million (S$63 million) worth of products to North Korea and imported US$3 million worth of goods last year (2016).

In August, Thai Foreign Minister Don Pramudwinai said that bilateral trade had dropped by 94 per cent over the past year, but did not give further details.

In a press statement released on Thursday (Dec 14) evening, the Thai Foreign Ministry said Mr Virasakdi "reiterated that Thailand has complied with the relevant (United Nations Security Council) resolutions which imposed sanctions on North Korea".

"Thailand supports the rising call by the international community on North Korea to return to the negotiation process in order to reduce tension and denuclearise the Korean Peninsula, which will lead to sustainable peace and security in the region", it said.

General Wanlop was cited by an AFP report saying Thailand had reduced its trade with North Korea to around US$1.5 million a year, and would also curtail visas to North Koreans.

Pyongyang is known to have sophisticated ways of evading sanctions, including using front companies or agents from other countries.

US Assistant Secretary for East Asian and Pacific Affairs Susan Thornton told reporters during a trip by US Secretary of State Rex Tillerson to Thailand in August that the US believes North Korean front companies are active in Thailand and is trying to encourage the Thais to shut them down.

She told reporters the US also encouraged Thailand to take as many North Korean refugees as it can handle.

Mr Tillerson on Tuesday (Dec 12) made the Trump administration's most direct overture for talks yet, saying he was open to sitting down with his North Korean counterparts for a first meeting "without pre-conditions". But a National Security Council spokesman later said Pyongyang must first "take sincere and meaningful actions towards denuclearisation".

On Sept 30 Mr Tillerson said the US was probing for a diplomatic opening, only to be slapped down publicly by Mr Trump, who tweeted that it would be a waste of time.

Former US negotiators sympathise with Mr Yun, whose authority to negotiate has been undercut by the tug-of-war between a White House "breathing fire" and a State Department pushing a peaceful solution, according to a Reuters report published in early November.

On Friday, Mr Yun reiterated that North Korea could ease the way for talks to begin if it took credible steps like halting missile tests.

Asked what the US will do to lower tensions, he said: "What do you want us to do?"