KHOST, Afghanistan, July 12 (UPI) -- A suicide car bomb attack on a checkpoint near Camp Chapman, adjacent to the city of Khost, Afghanistan, killed 25 people on Sunday, according to reports.
No groups have claimed responsibility for the bombing.
The incident comes after U.S. drone strikes in Afghanistan's Nangarhar province, just north of Khost province, last week killed the commander of the region's Islamic State cell, Hafiz Saeed Khan, as well as two of the group's senior commanders.
Earlier last week, an improvised explosive device attached to a motorcycle killed two civilians and a police officer as a police unit patrolled by in Kandahar, and a suicide car bomb attack on a NATO convoy in Kabul wounded four civilians.
Sunday's attack also comes amid an increase in militant assaults on Afghan security forces, about 330 of whom are killed or wounded each week in militant attacks by the Taliban and other groups, according to U.S. and Afghan officials. In the first 15 weeks of 2015, such attacks occurred at a rate 70 percent higher than during the same period in 2014.
The Taliban claimed to have killed up to 25 police officers in raids against checkpoints -- some manned by two to three officers -- in remote areas of Helmand province last month.
Around the same time, the Afghan military says it counter-attacked and seized two districts in the county's north after they were overran by Taliban militants fighting alongside IS forces.
U.S. President Barack Obama announced plans for U.S. withdrawal from Afghanistan in 2011, and coalition forces officially handed the security operation to Afghan forces in December 2014.
The president's original timetable called for a reduction of U.S. troops in the country to 5,500 by the end of 2015, but in late March Obama announced the U.S. force would maintain its current posture of nearly 10,000 troops, used for advising and assisting Afghan forces, until the end of the year.
Camp Chapman was the setting of a 2009 attack, when an al-Qaida triple agent blew himself up while meeting with CIA handlers, killing nine people, including seven officials working for the agency.