Twenty-five Ethiopian migrants are missing off war-torn Yemen after being forced into the sea, the United Nations migration agency said Friday, highlighting the dangers of a well-traveled route from the Horn of Africa to rich Gulf nations.

Director of operations and emergencies Mohammed Abdiker said in a Twitter post that people in the last of four boats carrying migrants were forced to swim to shore Thursday as they approached Yemen's Shabwa province from Somalia.

No bodies have been found.

About 600 Ethiopian migrants, men and women, were aboard the boats, spokesman Joel Millman said — an unusually large number of migrants to arrive off Shabwa at one time.

International Organization for Migration figures show that some 87,000 people sought to reach Yemen from the Horn of Africa by boat in 2017.

U.N. agencies have attempted to discourage migrants from countries such as Ethiopia and Somalia from embarking on the perilous trip. But many are drawn to attempt the journey to rich Gulf countries beyond Yemen to find work, and there is no central authority to prevent them from travelling through the impoverished country where civil war has raged since early 2015.