* U.N. force launched offensive against rebels last week
* Rwanda denies backing M23 rebellion (Adds details, context)
By Jenny Clover
KIGALI, Aug 29 (Reuters) - Two people were killed when an artillery shell crashed close to a Rwandan market near the border with Democratic Republic of Congo on Thursday, residents in the Rwandan frontier town of Gisenyi said.
A Rwandan official confirmed the deaths and said a second shell had landed inside Rwanda near a border crossing, seriously wounding one person.
Last week, a 3,000-strong U.N. intervention brigade with a mandate to neutralise armed groups launched an operation in eastern Congo against a rebel group widely believed to be backed by Rwanda.
"The bomb killed two people, a woman and a baby," witness Nizeyimana Hamis told Reuters by telephone.
The Rwandan official who spoke on condition of anonymity accused the Congolese army of firing the shells. Rwanda denies backing the so-called M23 rebellion but fears are growing the violence inside Congo could spill across borders.
A diplomat in the Great Lakes region told Reuters it was clear the rebels had received support from Rwanda to help counter the U.N. force's aerial and ground assault over the past week. (Reporting by Jenny Clover in Kigali and Richard Lough in Nairobi, editing by George Obulutsa and Elizabeth Piper)