A heated political row has broken out in the US amid the ongoing investigation into alleged links between associates of Donald Trump and Russia during last year's election campaign.

President Trump - who has been struggling to shake off the Russia controversy in recent weeks - yesterday said he felt "somewhat" vindicated following an announcement by the Republican chairman of the congressional committee investigating the matter.

Devin Nunes revealed that he had seen reports suggesting information from the Trump transition team was "incidentally" collected during wider surveillance efforts - an announcement prominent Democrats quickly criticised as an "act of diversion".

Mr Nunes told reporters: "I recently confirmed that on numerous occasions the US intelligence community incidentally collected information about US citizens involved in the Trump transition."

He also claimed that "details with little or no apparent foreign intelligence values were widely disseminated in intelligence community reporting".

"I want to be clear, none of this surveillance was related to Russia or the investigation of Russian activities or [of] the Trump team," he explained.

Mr Nunes stressed: "I believe it was all done legally, I think it was all obtained legally."

The comments - which were light on specific details - did not appear to support Donald Trump's unsubstantiated allegations that Trump Tower was 'wiretapped' by Barack Obama.

Prominent officials - including FBI director James Comey, NSA head Mike Rogers, and even Nunes himself - have publicly said they have seen no evidence to back up the president's allegations.

However, the announcement by Mr Nunes will likely prove a source of relief for the Trump administration in their public efforts to draw attention away from the FBI investigation.

Mr Trump has repeatedly claimed attention should be focused on high-profile leaks from Washington.

The real story that Congress, the FBI and all others should be looking into is the leaking of Classified information. Must find leaker now!

— Donald J. Trump (@realDonaldTrump) March 20, 2017

Mr Nunes - who was part of the Trump transition team - briefed the White House on his announcement yesterday.

President Trump later said: "I very much appreciated the fact that they found what they found." He said he felt "somewhat" vindicated.

Mr Nunes's announcement came two days after the FBI confirmed that it is investigating any possible links between members of the Trump campaign and the Russian government.

Democrat response

The substance and potential impact of Mr Nunes's allegations remain unclear.

Writing in The Atlantic, David A Graham called the announcement a "head-spinning development," suggesting "Nunes’s vague statements raised a host of questions".

Democrats also questioned the significance of the Republican's claims, and reacted furiously to the decision to brief the White House and reporters. 

In a statement, Adam Schiff - the ranking Democrat on the house intelligence committee - said: "If accurate, this information should have been shared with members of the committee, but it has not been.

"I have expressed grave concerns with the Chairman that a credible investigation cannot be conducted this way."

He added: "Because the committee has still not been provided the intercepts in the possession of the Chairman, it is impossible to evaluate the Chairman's claims. It certainly does not suggest - in any way - that the President was wiretapped by his predecessor."

Speaking on NBC's Meet the Press last night, Mr Schiff claimed he had seen evidence to substantiate allegations that associates of President Trump colluded with Russia during the election campaign.

Mr Schiff announced: "I don't want to get into specifics but I will say that there is evidence that is not circumstantial and is very much worthy of an investigation." He revealed no further details.

Several other Democratic politicians also criticised Mr Nunes, with house minority leader Nancy Pelosi saying: "The unprecedented comments of Chairman Nunes are an act of diversion and desperation. The Chairman’s highly irregular conduct with the White House raises serious questions about his impartiality, especially given his history as part of the Trump Transition team.

"Abandoning any pretense of bipartisanship, Chairman Nunes raced to the White House and to the press to perpetuate the Trump Administration’s misinformation campaign [...] Chairman Nunes is deeply compromised, and he cannot possibly lead an honest investigation." 

She called for a full independent and bipartisan commission into any possible Trump-Russia ties. 

Senator Elizabeth Warren, meanwhile, argued: "The idea that Devin Nunes will investigate Trump/Russia is a farce".

Who does House Intelligence Committee Chairman Devin Nunes think he works for: the American people or @realDonaldTrump?

— Elizabeth Warren (@SenWarren) March 23, 2017

This is not the first time there have been calls for an independent investigation.

After Mr Nunes last month said he had yet received any evidence of Trump ties with Russia, Senator Bernie Sanders argued: "It doesn't matter to me what the administration says, it doesn't matter to me what Congressman Nunes says. What matters to me is the American people have got to learn the truth, and that means an independent investigation."