KABUL, Afghanistan — In what was an extraordinarily violent day even by Afghan standards, separate incidents on Sunday killed seven Western troops, including six Americans who died in a single blast, along with five Afghan police officers and at least 18 civilians, Western and Afghan officials said.

The six Americans died in an explosion in eastern Afghanistan, where fighting has been on the increase. The North Atlantic Treaty Organization force confirmed the deaths late Sunday without disclosing the nationality of those killed, but a U.S. official said they were Americans.

In recent months, the pace of military deaths caused by homemade bombs, had slowed, mainly because of better equipment and improved detection methods.

Two other Western troops were killed over the weekend in southern Afghanistan, the military announced: one in an insurgent attack Sunday, making it one of the year’s deadliest days for NATO forces; and another in a bombing Saturday.

The 18 civilians died in three separate explosions in a small district: Arghistan, in Kandahar province, close to the Pakistani border. In a cruel cascade of events, the first bomb tore through a minivan packed with early morning travelers on a rural road, and the second struck villagers who rushed to the rescue. The third hit yet another civilian vehicle a short distance away and a short time later.

At least five of the dead were women, according to provincial spokesman Ahmad Javed Faisal.

Underscoring insurgents’ determination to stage a comeback in Kandahar province, their traditional heartland, a band of insurgents stormed a police checkpoint in the district of Musa Qala in Helmand province just after dawn Sunday, the governor’s office said.

Casualties in the initial fighting were lopsided — 22 insurgents killed and three policemen wounded, according to provincial authorities. But an additional five policemen were killed by a roadside bomb after the police at the checkpoint called for reinforcements, according to Daoud Ahmadi, a spokesman for the governor.

Roadside bombs kill hundreds of Afghan civilians every year and maim thousands more. They are almost always planted by insurgents who intend them for coalition troops. Military patrols and civilian vehicles use the same roads, but it is most often noncombatants — who tend to travel in crowded, rattletrap vehicles — who bear the brunt of the blasts.

More than 3,000 Afghan civilians were killed last year in violence attributed to the conflict.

The pace of noncombatant fatalities dropped off sharply in the early months of this year as Afghanistan experienced its harshest winter in many years, but civilian deaths have soared in recent weeks after temperatures warmed and the summer “fighting season” heated up.

laura.king@latimes.com

Yaqubi is a special correspondent.