There are suggestions tension between United States President Donald Trump and First Lady Melania Trump may be thawing after they made a rare public show of affection while attending a key meeting about the US opioid epidemic.

The frosty body language between the presidential pair has long been analysed, but on Tuesday (Monday US time) they showed a united front while boarding a Marine One helicopter to attend an opioid crisis summit in New Hampshire.

Walking across the White House lawn, Mrs Trump, wearing high-heeled boots, had a stumble but was rescued by her quick-thinking husband, who prevented her fall.

Mrs Trump appeared to thank her husband for coming to her aid, placing an arm around his back in an uncharacteristically affectionate gesture from a First Lady who has famously public rebuffed her husband’s attempts at physical contact.

After later addressing the summit, Mrs Trump introduced her husband and warmly welcomed him to the stage with applause and a kiss on the cheek, before Mr Trump thanked his wife for being “so incredible”.

“We are blessed to have you as our First Lady,” he said. “We really are.”

It follows reports the Trumps’ marriage is in strife after the resurfacing of Mr Trump’s alleged affair with adult film star Stormy Daniels (real name Stephanie Clifford) in 2006, when Mrs Trump was pregnant with their son, Barron.

Mr Trump has consistently denied having an affair with Ms Daniels.

Mrs Trump withdrew from the public eye earlier this year after a Wall Street Journal report in January claimed Mr Trump’s lawyers had paid Ms Daniels $US130,000 ($A168,000) to stay quiet about an “intimate” encounter she had with the now-President.

US media speculated Mrs Trump would continue to lie low ahead of the upcoming March 25 airing of Ms Daniels’ tell-all interview with US 60 Minutes host Anderson Cooper, but her appearance at the opioid summit suggests otherwise.

Ms Daniels is reportedly being pursued by Mr Trump’s lawyers for damages after she allegedly violated a non-disclosure agreement she signed before the 2016 presidential election.

The White House has maintained Mr Trump had nothing to do with the agreement, nor the alleged payment to Ms Daniels.

Earlier this month, Ms Daniels field her own lawsuit seeking to invalidate the 2016 non-disclosure agreement on the basis it is “null and void” because Mr Trump himself never signed it.

Mrs Trump has never publicly commented on her husband’s alleged affair.