(CNN) -- Smugglers carrying a boatload of migrants forced their passengers to jump overboard in deep water off the coast of Yemen, causing up to 17 to drown, the United Nations said Tuesday.

The 52 Somali and Ethiopian passengers in one of seven boats crossing the Gulf of Aden were made to jump after the smugglers spotted police and refused to sail closer to shore, the U.N's refugee agency UNHCR said in a statement.

It said 35 people made it to land, six drowned and 11 others were missing presumed dead.

Almost 10,000 people have made the perilous journey across the Gulf of Aden to Yemen this year. Forty-seven people have died, with 23 bodies buried and 24 missing at sea, the UNHCR said.

Last year, more than 50,000 people crossed the gulf into Yemen.

Many are fleeing the war in Somalia, but recent months have seen an increase in the number of refugees from Ethiopia.

Yemen is a common destination for Somalis fleeing economic hardship and war because of its proximity. It is also an attractive location because Somalis receive automatic refugee status in the fellow Muslim country.

But according an article in the Yemen Post newspaper last year, the country is just a stopping point for most of the refugees, who then travel on to the wealthier Persian Gulf states, Europe or the United States.

In 2008, Yemen's coast guard stepped up patrols of its coastline to deter the smugglers. Some of the boats seized by Yemen's coast guard are given to Somali fishermen who suffered losses in the December 2004 Indian Ocean tsunami.

As part of a $19 million operation, UNHCR operates shelters and reception centers for the refugees in Yemen and has increased its efforts to discourage people from making the illegal sea crossing. It has also sponsored training programs for coast guard personnel and other officials.

The plight of the refugees has been overshadowed by the dozens of pirate attacks off Somalia's coast that have grabbed international headlines in recent months, according to the aid group Doctors Without Borders.

"A lot of attention has been paid lately to tackling the issue of piracy in the waters off the Horn of Africa," the organization's Yemen mission leader Francis Coteur said in November.

"Unfortunately, little attention is paid to the drama of the refugees crossing the same waters in horrific conditions. Much more needs to be done to address this issue."