Senator Lindsey Graham, the South Carolina Republican who is an outspoken supporter of Mr. Trump but sometimes tries to push him to more hawkish positions — such as opposing his plan to pull out of Syria — said on Twitter that he wanted the administration to take the intelligence assessment seriously and brief Congress on the matter.
“I expect the Trump Administration to take such allegations seriously and inform Congress immediately as to the reliability of these news reports,” Mr. Graham wrote.
The United States concluded months ago that the Russian intelligence unit, which has been linked to assassination attempts and other covert operations in Europe intended to destabilize the West or take revenge on turncoats, had covertly offered rewards for successful attacks last year.
In response to the intelligence assessment, senior administration aides developed an array of potential options — starting with making a diplomatic complaint to Moscow and a demand that it stop, along with an escalating series of sanctions and other more aggressive possible responses, according to officials familiar with internal deliberations.
But the White House has yet to decide on taking any step, the officials said in recent days.
Islamist militants, or armed criminal elements closely associated with them, are believed to have collected some bounty money, the officials said. Twenty Americans were killed in combat in Afghanistan in 2019, but it was not clear which killings were under suspicion.
The officials familiar with the intelligence did not explain the White House’s delay in deciding how to respond to the intelligence about Russia.
Afghanistan has been the site of proxy battles between Washington and Moscow before. In the 1980s, while the Soviet Union was mired in its own bloody war in the country, it was the United States that covertly helped arm the mujahedeen to fight against the Red Army in one of the last major confrontations of the Cold War.
After the Sept. 11, 2001 terrorist attacks, Russia was largely supportive of the American effort to destroy Al Qaeda and topple the Taliban government. Russia declared the Taliban a terrorist organization in 2003, but recently their relationship has been warming, with Taliban leaders traveling to Moscow for peace talks.
Fatima Faizi contributed reporting from Kabul, Afghanistan.