President Donald Trump's campaign and Russia did not collude during the 2016 presidential election, the House Intelligence Committee's Republicans said in a draft assessment of Russia's alleged efforts to steer the US poll.

The Republican's preliminary findings come as special counsel Robert Mueller continues to head a separate investigation into Russia and possible collusion with the Trump campaign that has shown signs of increasing intensity over the past few weeks.

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The ranking Democrat on the committee, Adam Schiff, slammed the Republicans for ending the investigation, calling the decision "a tragic milestone for this Congress".

"By ending its oversight role in the only authorised investigation in the House, the majority has placed the interests of protecting the president over protecting the country," he said in a statement. "History will judge its actions harshly."

The Republican's findings fit perfectly with Trump's oft-repeated narrative of the events. In a capital letter-laden tweet, Trump lauded the Republican determinations.

THE HOUSE INTELLIGENCE COMMITTEE HAS, AFTER A 14 MONTH LONG IN-DEPTH INVESTIGATION, FOUND NO EVIDENCE OF COLLUSION OR COORDINATION BETWEEN THE TRUMP CAMPAIGN AND RUSSIA TO INFLUENCE THE 2016 PRESIDENTIAL ELECTION. — Donald J. Trump (@realDonaldTrump) March 13, 2018

Report conclusion

Republicans on the committee found "a pattern of Russian attacks" on the US and Europe that included Moscow's cyberattacks on American political institutions from 2015-2016 as well as Russia's "use of social media to sow discord".

But they "found no evidence of collusion," Representative Mike Conaway, who was leading the probe, told reporters at the Capitol. "We disagree with the narrative that they were trying to help Trump."

The investigation is closed.

The full report will not be made publicly available until the panel's Democratic members are given the opportunity to review the findings and the intelligence community clears them for public release.

The committee's Democrats will receive the report Tuesday for review.

Other investigation

A separate investigation being taken up in the Senate is also continuing its inquiry, and shortly before the House panel released its findings, Senator Chris Coons said the Senate Intelligence Committee "continues to make solid progress" while ripping its House counterpart.

Conaway insisted that even though the Mueller probe is ongoing, the House committee had "the information necessary to support the conclusions we've come to".

"It is truly disappointing that the House Intelligence Committee is just hanging up its cleats, having not really run the race," he told CNN.

Conaway defended the House committee's decision to end their probe, telling Fox News that Coons' assessment is "uninformed at best".