Top officials said Monday that the U.S. needs to confront Russia for providing arms to the Taliban in the wake of a devastating attack on an Afghan army base.

Speaking to reporters in Kabul, Afghanistan, Defense Secretary James Mattis and Gen. John Nicholson did not get into specifics of Russia’s role in Afghanistan.

But Nicholson said he is “not refuting” reports that Russia is supplying weapons to the Taliban while Mattis said the United States would need to confront any behavior that violates international law, such as arming insurgents.

“Arming belligerents or legitimizing belligerents who perpetuate attacks like we saw two days ago in Mazar-i-Sharif is not the best way forward to a peaceful reconciliation,” said Nicholson, the top U.S. commander in Afghanistan.

ADVERTISEMENT

On Friday, more than 100 people were killed when gunmen disguised as soldiers attacked an army base outside Mazar-i-Sharif in northern Afghanistan. The rampage, likely the deadliest in the 16-year war, happened as unarmed Afghan soldiers were emerging from Friday prayer and heading to lunch.

The Taliban has taken credit for the attack. On Monday, Nicholson said it was “quite possible” the Pakistan-based, Taliban-linked Haqqani network was responsible, based on the “level of sophistication” of the attack.

Asked about Russia’s involvement in Afghanistan, Mattis said the United States would engage diplomatically with Russia where it can but stressed the administration must confront violations of international law.

“We’re going to have to confront Russia where what they’re doing is contrary to international law or denying the sovereignty of other countries,” Mattis said. “For example, any weapons being funneled here from a foreign country would be a violation of international law unless they’re coming through the government of Afghanistan for the Afghan forces, and so that would have to be dealt with as a violation of international law.”

U.S. officials have been voicing concern about Russian support for the Taliban for months.

In February, Nicholson told the Senate Armed Services Committee that Russia has been trying to legitimize the Taliban by promoting a false narrative that it is fighting the Islamic State in Iraq and Syria (ISIS).

And last month, Gen. Joseph Votel, commander of U.S. Central Command, told the House Armed Services Committee it is “fair to assume” that Russia is proving arms to the Taliban.

Mattis made his first trip to Afghanistan as Defense secretary Monday as the Trump administration determines how best to move forward in the country.

Nicholson has said he needs “a few thousand” more troops to break what he has described as a stalemate.

Mattis said Monday the situation will be “addressed” but would not elaborate on his own recommendations, saying he owes "some degree of confidentiality" to the deliberations.

He also said this year will continue to be a difficult one in the country.

Mattis said “2017’s going to be another tough year for the valiant Afghan security forces and the international troops who have stood and will continue to stand shoulder to shoulder with Afghanistan against terrorism and against those who seek to undermine the legitimate, United Nations recognized government of the this nation.”