DUBAI, United Arab Emirates: Migrants making their way from the Horn of Africa to Yemen are frequently abducted and tortured by "criminal gangs", the U.N. Migration Agency warned Monday.

Despite a war that has killed thousands and pushed Yemen to the brink of famine, some 6,000 migrants enter the country every month, according to the U.N.'s International Organization for Migration (IOM).

They often come from Ethiopia and Somalia, hoping to make their way overland to the more prosperous Gulf countries to find work.

Many are abducted by criminal gangs upon arrival in Yemen and tortured for ransom, according to IOM.

"A common technique is to call the migrant's family while allowing burning plastic from an empty water bottle [to] drip on a migrant's skin causing burns and excruciating pain," said IOM director general William Lacy Swing.

"Families usually pay up quickly and the migrants continue their journey often to be extorted repeatedly by different gangs before reaching their destination."

Dozens of migrants have died in the journey to Yemen this year alone.

In August, at least 50 Somali and Ethiopian migrants were deliberately drowned off Yemen by smugglers who appeared to have spotted the coastguard stationed along the coast of Shabwa in the Arabian Sea, according to the United Nations.