Two people - a priest and a nine year-old girl - were killed and 16 injured when a grenade was thrown into a Roman Catholic church congregation during an open-air mass being held at a school on Sunday morning in the eastern Democratic Republic of the Congo (DRC) city of Goma, news agencies reported.

"An individual who has not yet been identified threw a grenade into the crowd at a communion service," Jean-Pierre Lola Kisanga, deputy spokesman of the Rwandan-backed Rassemblement congolais pour la democratie (RCD-Goma) armed opposition movement that controls eastern DRC, was quoted as telling Reuters on Sunday. He told AFP that the motive of the attack remained unknown. Bizima Karaha, RCD-Goma security chief, told the BBC he believed the attack was politically motivated, and was intended to further derail the peace process.

Four suspects believed to be involved in the attack were being questioned by the RCD, AFP reported.

Goma, which borders Rwanda and was devastated by a volcanic eruption in mid-January, is under the control of rebels of the RCD-Goma, who have been fighting the Kinshasa government since 1998.

Recent ceasefire violations have hampered ongoing Congolese peace talks taking place in Sun City, South Africa. The Kinshasa government left the talks last week after RCD-Goma captured the eastern town of Moliro. However, it rejoined the talks on Thursday after both it and the rebels agreed to withdraw from positions captured in the past month.

The attack occurred just as the bishop of Goma arrived to celebrate the mass, the BBC reported.