An attack has taken place on the Camp Bastion military compound in Afghanistan, causing some injuries and damage.
Early indications were that the assault was on the north-east side of the base in Helmand Province, in the south of the country, which houses American forces in Camp Leatherneck.
A Ministry of Defence spokesman in London said: "We are aware of an incident that has taken place at Camp Bastion, which is currently being dealt with."
A spokesman for the Isaf coalition in Afghanistan said: "I can confirm there was an attack involving small arms fire. It has caused some injuries and damage."
It was later reported that at least two Americans had been killed in the attack on the Nato base. They are thought to have been Marines.
Prince Harry is currently based at Camp Bastion on his second tour of duty in Afghanistan, which is due to last four months.
He has been undergoing training to fly operations in Apache attack helicopters.
The 27-year-old Army captain arrived in the war-torn country last Friday, but will not have started his role yet as co-pilot gunner.
Camp Bastion is a huge base in the middle of the desert shared with US, Estonian, Danish and Afghan troops.
It is the logistics hub for operations in Helmand, with supply convoys and armoured patrols regularly leaving its heavily-defended gates, to support the military forward operating bases, patrol bases and checkpoints spread across Helmand province.