In the ten months since its stunning capture of Mosul, Iraq's second-largest city, the Islamic State has expanded its reach beyond its geographic base, establishing a foothold in countries such as Libya. A vicious suicide attack in Afghanistan now raises fear that the war-torn country may be next. On Saturday, an unidentified man detonated explosives inside a crowded bank in Jalalabad, a city located near the country's border with Pakistan, killing 33 and injuring over 100. The number of the dead, who were all civilians, is expected to rise.

Appearing on national television after the attack, Afghanistan president Ashraf Ghani claimed that a local affiliate of the Islamic State, also referred to by its Arabic acronym Daesh, was responsible.

"Taliban did not claim responsibility, but Daesh claimed responsibility," he said.

The involvement of ISIS has not been independently confirmed. But if Ghani is correct, Saturday's attack is an ominous development in a country struggling to combat a brutal insurgency from the Taliban, an indigenous Afghani group recently strengthened by an influx of foreign fighters.

On Saturday, a Taliban spokesman denied responsibility for the attack. But the group remains a lethal presence in Afghanistan. According to the Council on Foreign Relations, Taliban violence claimed the lives of over 8,600 civilians in 2013 alone, and the group threatens government control of an estimated 40 percent of the country's 373 districts. A military crackdown on Islamic extremism in Pakistan has caused militants to cross the border into Afghanistan, where they have found refuge with the Taliban. With the onset of spring—the traditional fighting season in Afghanistan—extremist violence will only intensify.

"Considering the influx of foreign fighters in Afghanistan, this fighting season will be the bloodiest fighting season," Atiqullah Amarkhel, a military analyst in Kabul, told the Washington Post.

Afghanistan's violence poses a significant problem for the Obama Administration, which seeks to wind down American involvement in the country. In March, Ghani persuaded Obama to maintain around 10,000 American soldiers in Afghanistan through the end of 2015—double the number that Obama had planned. Additional revisions to Obama's plan appear likely.

"We need to re-examine the pace and scope of the drawdown, in light of what we're going to need in the future," Michèle Flournoy, former undersecretary of Defense for policy, said earlier this year.

Despite the presence of international troops, Afghanistan's future nevertheless seems destined to involve ISIS. In January, the group identified Afghanistan and Pakistan—a region referred to as "Khorasan"—as integral to its plans to establish an Islamic caliphate. Impoverished and unstable, the country has long been a fertile ground for extremist politics—a situation that the U.S.-led military coalition has been powerless to stop.