WASHINGTON (REUTERS) - United States Republican presidential front-runner Donald Trump took a detour from the campaign trail on Thursday and held an unexpected meeting in Washington with Reince Priebus, the head of the Republican National Committee (RNC).

It was not immediately clear what the two men discussed but the meeting came after months of tension between Mr Trump and the party he seeks to represent in the Nov 8 election.

Mr Trump, who also has sought to contain the fallout from his Wednesday comments supporting punishment for women who have an abortion, said on Twitter afterwards that he had a "nice meeting" with Mr Preibus, but divulged no details.

"Looking forward to bringing the party together," he said."And it will happen!"

Mr Priebus said the meeting was scheduled days ago and included a discussion about the process heading into the party's July convention in Cleveland. Mr Trump leads the Republican race, but is at risk of falling short of the 1,237 delegates needed to become the party's nominee in the Nov 8 election, raising the prospect of a contested convention.

"We did talk about unity and working together and making sure when we go to Cleveland, and come out of Cleveland, that we're working in the same direction," Mr Priebus told the Fox News Channel.

He refused to say if the discarded loyalty pledge was discussed at the meeting with Mr Trump, which lasted just under an hour.

An RNC spokesman described the meeting as "a productive conversation about the state of the race" and said it was part of Mr Preibus' regular communications with the party's presidential candidates.

Mr Trump this week abandoned a pledge to support the eventual Republican nominee if it is not him.

He has also complained about the party's delegate allocation process as he seeks to win the 1,237 delegates necessary for the nomination.

"Just had a very nice meeting with @Reince Priebus and the #GOP. Looking forward to bringing the Party together -- and it will happen!" Trump wrote on Twitter.

Mr Barry Bennett, an adviser to the Trump campaign, said on MSNBC that the meeting was about Trump helping the RNC raise money.

"The meeting is to help the RNC," he said.

On Tuesday, Mr Trump backed away from a loyalty pledge he signed in September promising to support the party's eventual nominee and not to run an independent campaign for the White House. The RNC pledge has unravelled as Mr Trump's remaining rivals, US Senator Ted Cruz of Texas and Ohio Governor John Kasich, also indicated they were unlikely to observe it if Mr Trump was the nominee.

Mr Trump also met his foreign policy team in the capital on Thursday after a series of statements by the billionaire businessman on national security issues that have drawn criticism.

A source who attended said the group discussed threats from militants from the Islamic State in Iraq and Syria (ISIS), nuclear proliferation, homeland security assessments and European security levels.

Mr Trump's campaign also announced it was setting up a Washington office to run its convention and delegate operations and work with the RNC and Congress. The campaign has been busy trying to dig out from under an avalanche of criticism over his comment that women should face punishment for getting an abortion if the procedure was outlawed, although he quickly reversed his stance.

In recent interviews, Mr Trump has declared the Nato alliance obsolete, described Saudi Arabia as too dependent on the United States and said Japan and South Korea may need to develop their own nuclear programmes because the US security umbrella is too costly to maintain.

In an MSNBC town hall on Wednesday night, Mr Trump did not rule out the potential use of nuclear weapons in Europe or the Middle East to combat Islamic State in Iraq and Syria (ISIS) militants.

"I would never take any of my cards off the table," he said.

Mr Max Boot, a conservative national security expert and member of the Council on Foreign Relations, wrote in Commentary Magazine this week that Mr Trump is "singularly unqualified to be commander-in-chief."

"With Trump in command, our enemies would have a field day - Moscow and Beijing must be licking their chops at his desire to abandon US allies in Europe and Asia - and our friends would face mortal threats. If that isn't the single biggest threat to US security, I don't know what is," Mr Boot wrote.