JOHANNESBURG, South Africa — The US government has warned against travel to a popular tourist island in Madagascar after reports of rioting and the mob killings of two European men.

A French national and a man with both Italian and French passports, as well as a local man, were attacked by a mob that reportedly suspected them of organ trafficking after a young boy's mutilated body was found on a beach on Nosy Be island, off the northwest coast of Madagascar.

The two Europeans were tortured and beaten before being thrown alive onto a bonfire on Ambatoloaka beach, a stretch of white-sand beach lined with hotels, according to local media reports. The local man's body was found a few miles away.

Government ministers on Friday traveled to Nosy Be, which means "big island" in the Malagasy language, to appeal for calm. Police reinforcements have been sent to the island, and a curfew is in place.

There have also been reports of violent protests in Hell-Ville, the main city on Nosy Be island also known as Andoany, though the situation is now calm, the US Embassy said in an emergency message to its citizens.

"Arson, looting and the mob killing of two foreign suspects held in police custody have also been reported," the note said. "US citizens currently in Nosy Be are advised to shelter in place should they witness any large gatherings or violence."

Other countries including Britain and France have advised against all but essential travel to Nosy Be.

“British nationals currently living in Nosy Be should stay indoors and follow local security advice,” the UK Foreign and Commonwealth Office said in a statement.

Tourism is an important source of revenue for Madagascar, which is already suffering as a result of a protracted political crisis. The first elections since President Andry Rajoelina overthrew his predecessor Marc Ravalomanana in 2009 are scheduled to be held later this month.