Four staff of British-based security firm Global Risk Strategies were killed and 15 wounded in an attack in Baghdad's fortified Green Zone yesterday, the company said today.
A spokesman said he had no more immediate information on the incident or the nationalities of the casualties.
"We believe it was indirect fire but we do not know whether it was a rocket or a mortar," a US military spokesman said.
Coalition sources said the casualties were believed to be Nepalese Gurkhas.
The Green Zone, a sprawling complex surrounded by blast walls, houses the American and British embassies and the interim Iraqi government and parliament.
Two loud explosions echoed from the Green Zone on Thursday and thick black smoke was seen rising above the compound.
Insurgents regularly fire rockets and mortars at the compound, and have detonated several suicide car bombs close to its entrances.
Last month, two suicide bombers blew themselves up in a cafe inside the Green Zone.