President Donald Trump has signed an executive order to help protect US elections from foreign interference, authorising sanctions against countries and other actors who seek to meddle.

The order instructs intelligence agencies to assess and report on any attempts to interfere in a US election, including the use of propaganda.

Based on their assessment of the validity and impact of that intelligence, bans and restrictions on suspected culprits would be imposed.

The president has been widely criticised for his response to alleged Russian meddling in the 2016 presidential election.

Special counsel Robert Mueller is investigating the possibility Russian meddling, which Moscow denied and Mr Trump dismissed as a “witch hunt.”

Under Mr Trump’s executive order, the intelligence community would have 45 days to make its assessment, and then the two departments would have 45 days to determine whether action is required, he told reporters on a conference call on Wednesday.

The State and Treasury departments would decide on appropriate additional sanctions to recommend and impose, he said.

Sanctions could include freezing assets, restricting foreign exchange transactions, limiting access to US financial institutions, and prohibiting US citizens from investing in companies involved, White House national security adviser John Bolton said.

He said sanctions could be imposed during or after an election, based on evidence gathered.

Mr Bolton said the order was necessary to ensure a formal process and authorisation for sanctions, but he said he was in talks with lawmakers about legislation as well.

“We think … that this is an important step for the president to take as the leader of the executive branch, but we’re perfectly prepared to speak with members of Congress who have proposed legislation,” he said.

National Intelligence Director Dan Coats said the directive was in response to alleged Kremlin interference in the 2016 presidential election.

He said the measure was being put in place to try to ensure the government is doing everything it can to prevent interference, report on any suspicious activity between now and the midterms in November, and to do a full assessment after the election that would trigger sanctions if necessary.

-with AAP