The ISAF said in a statement Sunday a person wearing an Afghan national police uniform fired on coalition forces, killing three service members.
The British Defense Ministry said two of the soldiers were attached to the 1st Battalion Welsh Guards and the third was with the Royal Corps of Signals, the BBC reported Monday.
The troops were shot and killed at a checkpoint in Helmand province as they were leaving a meeting with local elders, the ministry said. The gunman was injured and detained.
"Their loss will be felt deeply across the task force. However, that will be nothing compared with the grief experienced by their families at home," a ministry spokesman said. "Our thoughts and prayers are with them at this extremely difficult time."
More than 20 coalition forces have been killed in similar shootings this year.