Afghan and Canadian forces moved into a series of villages outside of southern Afghanistan’s largest city on Wednesday to root out any Taliban who have infiltrated the area, and four British troops were killed by an explosion in Helmand province.

Troops exchanged fire with militants during “a few minor contacts” but there were no immediate reports of casualties, NATO spokesman Mark Laity said. Helicopters patrolled the skies and smoke rose from fields after exchanges of fire.

“As of this morning we’ve expanded operations into Arghandab,” Laity said. “Canadian troops are in support” of the Afghan National Army.