General Mark Milley, chairman of the Joint Chiefs of Staff, and Defense Secretary Mark Esper spoke before a congressional committee as the Trump administration comes under pressure to explain media reports claiming the president was briefed on the intelligence -- but did nothing in response.

Milley said the information was "not corroborated."

"We'll get to the bottom of it. We are going to find out if, in fact, it's true. And if it is true, we will take action," he continued, without specifying what kind of action might be taken.

Washington has known for years that Russia has been supporting the Afghan insurgents, including through arms shipments, Milley said.

But, in the case of the Russians, "we do not have concrete corroborating evidence, intelligence to show directing. That's a big difference," he said.

"All the defense intelligence agencies have been unable to corroborate that report," Esper agreed.

Even so, he added: "The commanders take all reports seriously, regardless of the degree of credibility or confidence."

The New York Times, followed by other US media, first reported on the intelligence last month.

The White House has said President Donald Trump was not briefed on the intelligence because it was unverified.

But the Times, citing multiple officials, reported the intelligence was included in the written presidential daily brief back in February.

The newspaper reported that US intelligence officers and special forces in Afghanistan began raising the alarm as early as January, and that the National Security Council held an interagency meeting in late March to discuss possible responses -- but the White House did not authorize any action.

Russia and the Taliban have denied the claims.

The scandal comes with Trump trying to withdraw troops from conflict-torn Afghanistan -- one of the Taliban's key demands -- and end America's longest war.

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THE NEW YORK TIMES COMPANY