WASHINGTON -- Eight Republican lawmakers attended a White House briefing about explosive allegations that Russia secretly offered bounties to Taliban-linked militants for killing American troops in Afghanistan -- intelligence the White House insisted the president himself had not been fully read in on.

Members of Congress in both parties called for additional information and consequences for Russia and its president, Vladimir Putin, and eight Democrats were to be briefed on the matter Tuesday morning, a day after the Republicans' briefing. Still, White House press secretary Kayleigh McEnany insisted Trump had not been briefed on the findings because they hadn't been verified.

The White House seemed to be setting an unusually high bar for bringing the information to Trump, since it is rare for intelligence to be confirmed without a shadow of doubt before it is presented to senior government decision-makers. McEnany declined to say why a different standard of confidence in the intelligence applied to briefing lawmakers than bringing the information to the president.

Republicans who were in the briefing Monday expressed alarm about Russia's activities in Afghanistan.

Rep. Michael McCaul, the ranking member of the House Foreign Affairs Committee, and Rep. Adam Kinzinger were in the briefing led by Director of National Intelligence John Ratcliffe, White House chief of staff Mark Meadows and national security adviser Robert O'Brien. McCaul and Kinzinger said in a statement that lawmakers were told "there is an ongoing review to determine the accuracy of these reports."

"If the intelligence review process verifies the reports, we strongly encourage the Administration to take swift and serious action to hold the Putin regime accountable," they said.

Rep. Liz Cheney, R-Wyo., and Texas Rep. Mac Thornberry, the top Republican on the House Armed Services Committee, said, "After today's briefing with senior White House officials, we remain concerned about Russian activity in Afghanistan, including reports that they have targeted U.S. forces."

Senators reviewed classified documents related to the allegations Monday evening. The information they received was not previously known, according to one aide who was not authorized to discuss the matter publicly and spoke on the condition of anonymity.

On CNN, House Speaker Nancy Pelosi confirmed the timing of the Democratic briefing but said "it's no substitute for what they owe the Congress of the United States." She said that "this is as serious as it gets."

She speculated that Trump wasn't briefed "because they know it makes him very unhappy, and all roads for him, as you know, lead to Putin. And would he tell Putin what they knew?"

The intelligence assessments came amid Trump's push to withdraw the U.S. from Afghanistan. They suggested Russia was making overtures to militants as the U.S. and the Taliban held talks to end the long-running war. The assessment was first reported by The New York Times, then confirmed to The Associated Press by American intelligence officials and two others with knowledge of the matter.

Republican Sen. John Cornyn told reporters Monday, "I don't think it's should be a surprise to anybody that the Taliban's been trying to kill Americans and that the Russians have been encouraging that, if not providing means to make that happen."

He added: "Intelligence committees have been briefed on that for months. so has Nancy Pelosi, so has (Democratic Senate leader) Chuck Schumer. So, this is, this is a more leaks and partisanship."

While Russian meddling in Afghanistan isn't new, officials said Russian operatives became more aggressive in their desire to contract with the Taliban and members of the Haqqani Network, a militant group aligned with the Taliban in Afghanistan and designated a foreign terrorist organization in 2012.

The intelligence community has been investigating an April 2019 attack on an American convoy that killed three U.S. Marines after a car rigged with explosives detonated near their armoured vehicles as they travelled back to Bagram Airfield, the largest U.S. military installation in Afghanistan, officials told the AP.

Three other U.S. service members were wounded in the attack, along with an Afghan contractor. The Taliban claimed responsibility for the attack on Twitter. The officials the AP spoke to also said they were looking closely at insider attacks -- sometimes called "green-on-blue" attacks -- from 2019 to determine if they are also linked to Russian bounties.

One official said the administration discussed several potential responses, but the White House has yet to authorize any step.

Intelligence officials told the AP that the White House first became aware of alleged Russian bounties in early 2019 -- a year earlier than had been previously reported. The assessments were included in one of Trump's written daily briefings at the time, and then-national security adviser John Bolton told colleagues he had briefed Trump on the matter. Bolton declined to comment, and the White House did not respond to questions on the matter.

The intelligence officials and others with knowledge of the matter insisted on anonymity to discuss the highly sensitive matter.

The White House National Security Council wouldn't confirm the assessments but said the U.S. receives thousands of intelligence reports daily that are subject to strict scrutiny.

Trump's Democratic general election rival, former Vice-President Joe Biden, used an online fundraiser Monday to hammer the president for a "betrayal" of American troops in favour of "an embarrassing campaign of deferring and debasing himself before Putin."

"I'm disgusted," Biden told donors, as he recalled his late son Beau's military service. Families of service members, Biden said, "should never, ever have to worry they'll face a threat like this: the commander in chief turning a blind eye."

Asked about the reports on the alleged bounties, Putin's spokesman Dmitry Peskov said Monday, "These claims are lies."

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Associated Press writer Deb Riechmann contributed to this report.