At least 21 people, including seven foreign troops, were killed on Monday in one of the deadliest days so far this year in Afghanistan, officials said in Kabul on Tuesday.

Five NATO soldiers were killed in a helicopter crash, while a land mine and mortar round killed at least six civilians in southern Afghanistan.

Meanwhile, the death toll in the shootout at a joint Afghan-US military base in eastern Afghanistan on Monday has risen to 10, officials said.

The melee at the base in Jalrez district of Wardak province occurred when a policeman opened fire at Afghan and US troops. Naqibullah Haidari, the District Governor, said at least 10 people were killed in the skirmishes.

He said the attacker, Nasir Ahmad, had been working as a police at the district police headquarters for more than a year. “He stood up on top of a police ranger and took control of the PK machine gun attached to the vehicle,” Mr. Haidari told DPA.

He said two US special forces, three Afghan policemen and three Afghan army commandos were killed in the shootout. Helicopters flying over the base killed two civilians and injured four others. He said the district police chief had also been injured, along with an officer and two Afghan interpreters for the foreign troops.

The incident in Wardak was the latest in a series of attacks on coalition forces by members of the Afghan forces. Last week, three Afghan soldiers opened fire on foreign troops outside a US base in Kapisa. A civilian NATO contractor was killed.

At least 62 foreign troops were killed in such incidents last year, compared to 35 in 2011.

The five soldiers killed late on Monday in the helicopter crash in the southern province of Kandahar were believed to be Americans, Provincial police chief Abdul Raziq said.

Bad weather and technical problems were likely the cause of the crash, Mr. Raziq said, noting the absence of insurgent activity in the area. NATO also said initial reports indicated no enemy activity.

In neighbouring Helmand province, a land mine exploded late on Monday under a tractor, killing four civilians, the Interior Ministry said. A mortar round also hit a house in Helmand, killing two civilians, it said.

The ministry blamed “enemies of Afghanistan,” a term it uses for Taliban militants, and said five women were among the civilians killed.