A Taliban attack on a mosque and dining facility at Camp Shaheen outside Mazar-e-Sharif in Afghanistan on Friday claimed the lives of more than 140 Afghan soldiers, with a final death toll still being tallied, prompting Afghanistan’s defense minister and army chief of staff to resign their positions.

“2017 is 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,” American Secretary of Defense, James Mattis, said upon his arrival in Afghanistan on Monday.  The storied Marine general turned Defense Secretary is in the country as a part of ongoing efforts to craft a new Afghan strategy against the likes of the Taliban.

Mattis told journalists that he was “under no illusions” about the problems facing the country, which may include an influx of weaponry reaching Taliban hands from American political opponent, Russia.  Even General John Nicholson, the head of U.S. and international forces in Afghanistan who recently testified before Congress that more troops were needed to end the stalemate against terrorists in Afghanistan, said he was “not refuting” reports that Russia was providing support, including weapons, to the Taliban.

A senior defense official who spoke under the condition of anonymity told reporters on Monday that intelligence indeed shows that Russia has been providing money and automatic weapons to the Taliban.  Russia has denied any such wrong doing, but claims they maintain open lines of communication with Taliban leaders in order to continue to push for peace talks.  They have also been openly critical of the United States and its ongoing efforts in the country.

Defence Minister Abdullah Habibi and Army Chief of Staff Qadam Shah Shahim “stepped down with immediate effect” following the Friday attack, which stands as the single deadliest Taliban attack in the long Afghan war against them.  The attack reportedly involved 10 jihadists approaching the base disguised as Afghan soldiers transporting their wounded.  They then detonated explosives once surrounded by hundreds of unarmed troops as they emerged from prayers.  The attack continued as they opened fire on new recruits in the area attending training.

Intelligence reports indicate that the Haqqani network, a wing of the Taliban based in Pakistan, was behind the attack.  The Taliban took responsibility for the attack within minutes however, but U.S. military officials believe doing so was intended to divert attention away from the Haqqani network, as implicating them would place increased attention on the other side of the Pakistani border.

Defense officials claim the attack likely took months to plan, indicating that the ten terrorists that entered the base may have received help from troops inside the Afghan military.  That would explain their awareness that soldiers would attend prayers without their weapons, making it the perfect time to strike.

U.S. officials likely don’t see the resignations as a surprise, as some called for them in March when militants entered the Afghan Army’s primary hospital and killed at least fifty people in a siege that was ultimately claimed by another terrorist organization operating in the region, ISIS.