MEXICO CITY: A clash between suspected members of rival drug gangs left 21 people dead on Thursday in a rural area of the Mexican state of Sonora, very close to the US border, Mexican justice officials said.

The clash involved "two groups of suspected drug traffickers and undocumented" migrants, the Sonora attorney general`s office said in a statement.

The fighting took place some 20 kilometers (12 miles) from the US border.

Police later detained nine people in the area, including six with bullet wounds, the statement said.

Northern Mexican border areas -- on key trafficking routes into the United States -- have seen some of the fiercest fighting between Mexico`s powerful drug gangs and with security forces in recent years.

Almost 23,000 people have died in a spiraling drug-related violence in the past three and a half years in Mexico amid a military crackdown on organized crime involving some 50,000 troops.

BDST: 10:16 HRS, July 2, 2010

NJ