U.S. President Donald Trump declared on Saturday 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, 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 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.

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 Trump and his legal team have examined presidential powers to pardon Trump aides, family members and possibly even himself.

Reuters has not confirmed the newspaper accounts.

"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," Trump wrote.

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

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

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

At the Senate confirmation hearings for his Cabinet position, Sessions initially failed to disclose his 2016 contacts with Russian Ambassador Sergei Kislyak and later said they were not about the campaign.

In March, Sessions recused himself from the Russia probe. During an interview with The New York Times this week, Trump lashed out at Sessions, saying he would not have chosen him for attorney general had he known Sessions would recuse himself.

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

"So many people are asking why isn't the A.G. or Special Counsel looking at the many Hillary Clinton or Comey crimes. 33,000 emails deleted...," he tweeted.

(Source: CNN)