After a series of mass shootings, Trump had expressed provisional support for expanding reviews for potential buyers to address a range of loopholes that allowed many sales to go unrecorded.

He told National Rifle Association head Wayne LaPierre Tuesday, according to media reports, that he would urge Congress to pass "red flag" laws allowing the temporary removal of guns from people seen as a risk to themselves or others.

But he said he would not lead the effort to establish a law preventing unreported and unreviewed sales that take place online and at gun shows, away from licensed weapons stores, the reports said, citing White House sources.

Trump's position is crucial, because congressional Republicans, who count on gun rights supporters for votes, cannot move on tougher firearms legislation without the president's support.

Democrats meanwhile cannot push legislation through Congress without the backing of Republicans, who control the Senate and the White House.

The White House had no official comment on the reports, which said Trump himself initiated the 30-minute phone call with LaPierre.

But the NRA chief confirmed the call on Tuesday, saying Trump is a firm supporter of the constitution's second amendment, which gun rights advocates says guarantees absolute, broad rights to purchase and own firearms without government interference.

"I spoke to the president today. We discussed the best ways to prevent these types of tragedies," he tweeted.

Trump "is a strong #2A President and supports our Right to Keep and Bear Arms!" LaPierre said, referring to the second amendment.

Speaking to reporters on Tuesday, Trump did not mention the call but said the United States has "very, very strong background checks right now."

He added that rules could be tightened for people with mental health issues.

"A lot of the people that put me where I am are strong believers in the Second Amendment, and I am also," he said.

"Democrats would, I believe, give up the Second Amendment," he said.