About 100 people are missing and feared drowned off the shores of Yemen after their smugglers forced them overboard in the treacherous Gulf of Aden waters, Yemeni officials and the UN refugee agency said on Friday.

In Geneva, the U.N. refugee agency spokesman Ron Redmond told reporters that the smugglers' boat had left Somalia on Monday with 150 people on board.

Later, as the vessel neared the coast of Yemen, the smugglers forced the migrants overboard, Redmond said. Only 47 survivors managed to swim 3 miles to the shore and alert authorities.

A local security official said the boat was bound for Yemen's Shabwa province, some 300 miles south of San'a on the Gulf of Aden coast. He believed that between 100 and 118 migrants could have drowned. The official spoke on condition of anonymity because he was not authorized to talk to media.

Yemen is a destination for migrants from the Horn of Africa, particularly from Somalia, where ongoing violence has killed thousands of civilians, and there have been frequent reports of drownings off its shores and abuse by smugglers. Often, migrants are attacked during the journey by smugglers and thrown overboard into shark-infested waters.

The U.N. high commissioner for refugees, Antonio Guterres, said Thursday that the number of crossings has doubled "in the present season."

So far this year, about 32,000 people have arrived in Yemen on boats, many of them from the Horn of Africa, he said. The UNHCR estimates at least 230 people have died and 365 remain missing, including 100 from the latest incident.

"This is one of the most dramatic situations in the world," Guterres said at a press conference in Geneva. "Rescue at sea is also one of the areas in which the world has to invest massively to be able to be more and more effective."

"The way smugglers and traffickers treat people is absolutely outrageous and corresponds to one of the worst crimes that we can see in today's world," Guterres said. "This is an area where I believe the international community needs to invest a lot in the management of borders, but the management of borders with a protection-sensitive approach."

He urged the international community to look "not only for pirates but also to look for these (human trafficking) situations in the Gulf of Aden."

The waters off Somalia have been plagued by pirate attacks, despite patrols by U.S. warships trying to protect shipping. This month, a Ukranian tanker full of heavy weapons was seized, and pirates demanding ransom still hold the ship.

In the Yemeni capital of San'a, the Interior Ministry said in a statement that 22,532 Somali migrants have reached Yemen so far this year.

During the first half of September, some 165 of the bodies that floated ashore have been buried in Yemeni soil, while hundreds are missing and feared dead, the ministry said.