US President Donald Trump declared today that he has "complete power to pardon," as his administration confronts ongoing investigations of possible ties between his 2016 campaign and Russia.

In a series of early morning Twitter messages, Mr Trump aired renewed frustration with his attorney general, the special counsel leading the Russia probe, and Republicans in Congress who are struggling to advance his legislative agenda.

But Mr Trump's comment about pardons, tucked into an attack on the media, raised the possibility that he was considering his options if the investigations do not turn out the way he hopes.

Mr Trump did not specify who, if anyone, he might consider pardoning. His tweets appeared to be written in response to a report by The Washington Post this week that Mr Trump and his legal team have examined presidential powers to pardon Trump aides, family members and possibly even himself.

While all agree the U. S. President has the complete power to pardon, why think of that when only crime so far is LEAKS against us.FAKE NEWS — Donald J. Trump (@realDonaldTrump) July 22, 2017

The Washington Post, citing current and former US officials, reported yesterday that Russia's ambassador to the United States was overheard by US spy agencies telling his bosses that he had discussed campaign-related matters with Trump adviser Jeff Sessions last year, when Sessions was a US senator.

Mr Sessions now leads the Justice Department as Trump's attorney general.

"These illegal leaks...must stop," Mr Trump tweeted.

Mr Trump, who defeated Democrat Hillary Clinton in last year's presidential election but continues to use her as a foil, questioned why Mr Sessions, and special counsel Robert Mueller were not investigating former FBI Director James Comey or Ms Clinton, for her email practices as secretary of state.

"So many people are asking why isn't the AG or Special Counsel looking at the many Hillary Clinton or Comey crimes. 33,000 emails deleted...," he wrote on Twitter.

"My son Donald openly gave his e-mails to the media & the authorities whereas Crooked Hillary Clinton deleted (& acid washed) her 33,000 e-mails!"

The FBI decided last year not to recommend criminal charges against Ms Clinton for her email practices. Mr Trump fired Mr Comey in May.

Mr Sessions had been Mr Trump's first supporter in the Senate before being named attorney general, but recently has become a lightning rod for the former businessman’s anger over the probe into allegations of Russia's meddling in the 2016 presidential election.

Mr Sessions recused himself from the probe in March after having failed to disclose at his confirmation hearing that he had held meetings last year with Russia's ambassador.

The US Senate Judiciary Committee said yesterday that Mr Trump's eldest son, Donald Trump Junior, and his former campaign manager Paul Manafort had agreed to negotiate whether to be interviewed by the panel in its Russia investigation.

Mr Trump also had words for Republican senators who have not been able to agree on a way forward to repeal and replace former president Barack Obama's healthcare law, the Affordable Care Act, which has become known as Obamacare and which Mr Trump promised to do away with as president.

"The Republican Senators must step up to the plate and, after 7 years, vote to Repeal and Replace. Next, Tax Reform and Infrastructure. WIN!" he tweeted.