A Nato plane crashed in Afghanistan on Saturday killing four service members, the coalition said, adding that early reports suggested the aircraft was not brought down by insurgents.
The plane crashed in the south of the country, according to a statement from Nato's International Security Assistance Force.
"The cause of the crash is under investigation, however initial reporting indicates there was no enemy activity in the area at the time of the crash," it said.
Most international soldiers in southern Afghanistan are from the United States, but the nationality of the dead was not released in line with coalition policy.
There was no immediate claim of responsibility from the Taliban, who earlier Saturday announced the start of their annual "spring offensive" vowing a nationwide series of attacks as NATO troops withdraw.
Aircraft crashes are fairly frequent in Afghanistan, where the 100,000-strong international mission relies heavily on air transport as it battles the insurgency across the south and east of the country.
Earlier this month, two US troops were killed when a NATO helicopter crashed in the eastern Afghanistan, while five US troops died in the southern province of Kandahar in March when their helicopter came down during a heavy rainstorm.
On Saturday, the Taliban said that their annual offensive would target international airbases and diplomatic buildings with multiple suicide bombings, "insider attacks" by Afghan soldiers and "special military tactics".
They warned Afghans working for President Hamid Karzai's "stooge" regime to distance themselves from the government to avoid being caught up in the promised violence, and called for young people not to join the police or army.
This year's "fighting season" is seen as crucial to Afghanistan's future as its much-criticised security forces pit themselves against the Islamist extremists who have fought against the Kabul government since 2001.
NATO combat operations in Afghanistan are due to end next year, and coalition commanders say that the local army and police have made enough progress to provide security and keep the Taliban at bay.
Last week a study by the Afghanistan NGO Safety Office found attacks by the Taliban and other insurgents rose 47 percent in January-March compared with the same period last year.
The United Nations has separately reported a rise of almost 30 percent in civilian casualties in the first quarter compared with the same period last year, with 475 civilians killed and 872 wounded.