Officials in southern Afghanistan say suicide bombers have killed at least 22 civilians in an attack on a parking lot where trucks wait to supply a nearby NATO air base.

Authorities say a bomber on a motorcycle set off the first blast Wednesday in Kandahar, and as people rushed to help the victims, a second bomber on foot detonated his explosives. The attacks wounded at least 50 other people.

The blasts happened near the Kandahar Air Field, a massive base run by the U.S.-led coalition.

There was no immediate claim of responsibility.

The United Nations Assistance Mission in Afghanistan released a report last week saying civilian casualties in Afghanistan remain at “unacceptably high levels.”

The continued violence has raised concerns about the ability of Afghan forces to handle security beyond 2014, when most NATO forces are planning to conclude their combat role.