Director of National Intelligence James R. Clapper Jr. speaks during a hearing of the Senate Armed Services Committee on Thursday. (Brendan Smialowski/AFP/Getty Images)

The top U.S. intelligence official said Thursday that he supports arming Ukrainian forces against Russian-backed separatists, as the Obama administration continues deliberations about whether to deepen involvement in a conflict pitting the West against Russian President Vladi­mir Putin.

James R. Clapper Jr., the director of national intelligence, said providing weapons to Ukraine would likely trigger a “negative reaction” from the Russian government, which Western officials are hoping will ensure that separatists stick to a European-brokered cease-fire that took effect this month.

“It could potentially further remove the very thin fig leaf of their position that they have not been involved in Ukraine,” Clapper told members of the Senate Armed Services Committee, adding that Russia could respond by sending more sophisticated weapons to separatist areas.

He said U.S. intelligence officials believed that Putin may also intend to expand Russian influence in eastern Ukraine by trying to secure a land bridge to the Crimean Peninsula or taking control of the strategic port in Mariupol.

Nevertheless, pressed by senators to reveal his position on proposals to provide “lethal assistance” to Ukrainian forces, Clapper said he would support it.

“From an intelligence community perspective, that is a policy issue,” Clapper said. “I would favor it, but that is a personal perspective, and it does not represent an official company policy of the intelligence community.”

The administration is under growing pressure from some lawmakers to provide lethal weaponry to Ukraine. President Obama has said he is considering doing so, and some members of his Cabinet are said to favor sending arms. The United States has already sent the Ukrainians non-lethal aid such as night-vision goggles, radios and body armor.

While European leaders expressed some hope the latest ceasefire proposal would push the conflict closer to an end, NATO’s top military commander, U.S. Air Force Gen. Philip M. Breedlove, said this week that fighting in eastern Ukraine was “getting worse every day.”

On Thursday, Lt. Gen. Vincent R. Stewart, who heads the Defense Intelligence Agency, appeared to differ with Clapper, telling lawmakers at the same hearing that U.S. weapons would not reach Ukrainian troops quickly enough and wouldn’t change the battlefield balance.

Opponents of sending lethal weapons to Ukraine are reluctant to see the United States drawn further into the worst European conflict since the Balkan wars, even as Putin increases economic pressure on Ukraine.

In a hearing focused on global threats to U.S. security, both officials raised flags about a host of other conflicts, including Afghanistan, where U.S. forces have shifted to a training role ahead of their planned withdrawal in 2016.

Even after years of U.S. and NATO support for Afghan security forces, Stewart said that Afghan police and soldiers “remain stalemated with the Taliban-led insurgency.”

“The Taliban will probably sustain the capability to propagate a rural-based insurgency that can project intermittent attacks in urban areas through at least 2018,” he said in his prepared remarks, well after the planned end to the U.S. military mission there.

The bleak assessment is a reminder of the challenges that remain as military leaders make the case for slowing the U.S. exit from Afghanistan, a key foreign policy priority for Obama. Clapper, in his own prepared testimony, said Afghanistan would continue to require outside help to fight “an increasingly aggressive” Taliban.

Clapper suggested a similar dynamic exists in Iraq, despite a growing U.S. force there scrambling to assist Iraqi troops against Islamic State militants.

“Over six months into the coalition campaign ... the frontlines against the group have largely stabilized,” Clapper said. “No side is able to muster the resources necessary to attain its territorial ambitions.”

The return to Iraq is an uncomfortable one for Obama, who made the decision to pull out all U.S. troops in 2011.

Stewart said it could be at least six months before Iraqi forces are ready to mount a campaign to recapture major Iraqi cities, such as Mosul, from the Islamic State. Last week, U.S. Central Command said a Mosul campaign could take place as early as April or May.

“When we talk about the six to nine months additional training, it is to deal with an urban fight, which is very, very different, very complex,” he said.