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GENEVA, March 26 (Reuters) - At least 29 people were killed and 71 reported missing after knife-wielding smugglers forced some 450 Somali and Ethiopian migrants into the sea off Yemen, the U.N. refugee agency (UNHCR) said on Monday.

The incident, the latest in a series involving smugglers' boats carrying people across the Gulf of Aden from Somalia, occurred last Thursday along a remote stretch of coastline.

"We are horrified by this latest tragedy," said UNHCR's Assistant High Commissioner Erika Feller.

"These brutal smugglers care nothing about the fate of the people they prey on."

Some of the 293 survivors and other witnesses said four smugglers' boats were approaching the coastal town of Ras-Alkalb when the crews forced the passengers overboard in rough seas and strong currents.

Those who resisted were stabbed and beaten with wooden and steel clubs, then thrown overboard where some were attacked by sharks, they said.

Thursday's attack brings to 262 the number of people killed or unaccounted for so far this year after attempting the crossing by boat to Yemen to escape violence and anarchy in Somalia, the agency said.

Smugglers, usually Somali, often drop migrants in deep waters because Yemeni authorities have increased sea patrols closer to shore.

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