HONG KONG (BLOOMBERG) - Secretary of State Michael Pompeo will arrive in Singapore for a regional summit that will spotlight the challenges facing US efforts to keep up international pressure against both North Korea and Iran.

Pyongyang has been sending representatives to meetings hosted by the Association of Southeast Asia Nations since 2000, but this year they'll enjoy enhanced diplomatic prominence after President Donald Trump's summit with Kim Jong Un in the city-state two months ago.

The Iranians, meanwhile, signed a friendship pact Thursday with a 10-member regional bloc.

Both nations are engaged in fraught disputes with the US over their weapons programmes and nuclear aspirations.

And both have seen success in courting global support despite Trump's effort to pressure them. Underscoring the issue: North Korean Foreign Minister Ri Yong Ho was slated to fly on to Tehran after the summit. He arrived on Friday (Aug 3) in Singapore on an Air China Ltd. plane.

Several close US allies, including France, Germany and the U.K., have criticised Trump's decision to withdraw from the nuclear deal with Iran. And Asean members resisted calls by Pompeo's predecessor, Rex Tillerson, to downgrade or sever diplomatic ties with Pyongyang last year at the height of Kim's provocations.

"When Asean countries look at countries like North Korea and Iran, they don't feel directly threatened by them, like say the US does," said Oh Ei Sun, senior adviser for international affairs at the Asian Strategy and Leadership Institute in Kuala Lumpur.

"We look at Iran like we look at North Korea - great trade and investment opportunities."

North Korea and Iran are at opposite ends of up-and-down relationships with the US, especially as illustrated by the president's tweets.

Trump last week warned Iranian counterpart Hassan Rouhani that he would "SUFFER CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED," if he threatened America.

On Thursday, Trump, who had unleashed similar rhetoric against Kim last year, instead praised the North Korean leader for returning the remains of about 55 US service members killed in the Korean War - the first tangible outcome since their summit.

"I am not at all surprised that you took this kind action," Trump said in a tweet.

Still, Pompeo has sought to maintain Trump's pressure campaign against North Korea as the two sides bicker over Kim's pledge to "work towards complete denuclearisation of the Korean Peninsula."

The secretary will remind all nations present of their commitments to maintain sanctions against North Korea until that goal is achieved, a senior State Department official said at a briefing Tuesday in Washington.

Fully Verified

In recent weeks, Pompeo has repeatedly asserted that Kim agreed to the "final, fully verified denuclearisation of North Korea", implying a more explicit intent to disarm.

The Asean Regional Forum on Saturday - including ministers from Asean and 16 other nations - could provide Ri the chance to offer North Korea's own interpretation.

"They will say that what they have agreed is to work toward denuclearisation of the Korean Peninsula and what they understand by that is a series of concessions of the part of America leading to a peace agreement," said Malcolm Davis, a senior analyst at the Australian Strategic Policy Institute in Canberra.

Iranian Foreign Minister Mohammad Javad Zarif wasn't expected to attend any gatherings including his US counterpart.

While Trump earlier this week offered to meet Rouhani with "no preconditions," Pompeo has outlined a list of demands - from halting its ballistic missile program to getting out of the war in Yemen - for Iran to become a "normal country".

More broadly, the secretary was expected to try to bolster US support in the region by promoting a US$113 million initiative to help fund energy, infrastructure and digital economic projects.

The plan was seen as the beginnings of an effort to counter China's multi-billion Belt and Road infrastructure plan and make amends for Trump's decision to withdraw from the Trans-Pacific Partnership trade deal.

"America doesn't do things like Belt and Road - it doesn't have a state directed investment like China does," said Ian Storey, a senior fellow at the ISEAS-Yusof Ishak Institute in Singapore.

"I expect Asean to cautiously welcome the initiative though, because it gives them a chance to hedge against China. Hedging is what Southeast countries do and have to do."