Trump slams ousted FBI director

President Donald Trump called ousted FBI chief James Comey a "showboat" and "grandstander," but its acting leader contradicted the president and promised the agency's probe into possible Trump campaign ties to Russia would proceed with vigour.

In his first interview since the abrupt dismissal, Trump also gave further details to NBC News of his account that Comey had told him on three separate occasions that he was not under investigation in the Russia matter.

Trump, facing Democratic accusations that he fired Comey on Tuesday to hinder the FBI investigation into alleged meddling by Russia in the 2016 US presidential election, said he would have taken the action even without a recommendation to do so by the two top Justice Department officials.

Azadeh Ansari reports from Washington DC on a confusing day of denial and contradiction.

The White House and Vice President Mike Pence have said Trump fired Comey on the recommendation of Attorney General Jeff Sessions and No. 2 Justice Department official Rod Rosenstein.

"He's a showboat. He's a grandstander," Trump said. "The FBI has been in turmoil. You know that I know that, everybody knows that."

During the interview Trump also said that he has given a letter to Republican Senator Graham saying he has no investments in Russia.

In testimony before the Senate Intelligence Committee, acting FBI Director Andrew McCabe, testifying in place of Comey, promised to tell the panel of any White House meddling into the agency's probe. Democrats have called for a special prosecutor to look into the Russia matter.

Former Republican Representative Mike Rogers is being considered as a candidate to replace Comey, a senior White House official said. The US Senate must confirm the nominee.

Trump signs executive order on cyber security

President Donald Trump signed an executive order on Thursday to bolster the US government's cyber security and protect critical infrastructure from cyber attacks, marking his first significant action to address what he has called a top priority.

The order seeks to improve the often-maligned network security of US government agencies, from which foreign governments and other hackers have stolen millions of personal records and other forms of sensitive data in recent years.

The White House said the order also aimed to enhance protection of infrastructures such as the energy grid and financial sector from sophisticated attacks that officials have warned could pose a national security threat or cripple parts of the economy.​

The directive, which drew mostly favourable reviews from cyber experts and industry groups, also lays out goals to develop a more robust cyber deterrence strategy, in part by forging strong cooperation with US allies in cyberspace.

White House homeland security adviser Tom Bossert said the order sought to build on efforts undertaken by the former Obama administration.

Among the notable changes, heads of federal agencies must use a framework developed by the National Institute of Standards and Technology to assess and manage cyber risk and prepare a report within 90 days documenting how they will implement it.

Kremlin optimistic after Trump-Lavrov meeting

The Kremlin feels cautious optimism about the prospects for an improvement in US-Russian relations after Russian Foreign Minister Sergei Lavrov met Trump in Washington, a Kremlin spokesman said on Thursday.

"The conversation itself is extremely positive," Kremlin spokesman Dmitry Peskov said.

Peskov said the Kremlin viewed the prospects of a thaw "with cautious optimism." "We have a lot of work ahead of us," he said.