The U.S.-Mexico border is the deadliest land crossing in the world, according to the International Organization for Migration’s (IOM) Missing Migrants Project. According to data published by IOM, at least 728 people died while trying to cross the U.S. southern border last year. This year, 493 migrants have already died, including 53 people found in an abandoned tractor trailer in San Antonio.

Many of the dead are from countries with high numbers of asylum seekers. 136 Venezuelans, 108 Cubans and 90 Haitians have died in the last 18 months trying to migrate to the U.S., but the IOM said the countries of origin for more than 500 dead migrants are listed simply as “unknown.”

“The number of deaths on the United States-Mexico border last year is significantly higher than in any year prior, even before COVID-19,” said Edwin Viales, author of the IOM report. “Yet, this number remains an undercount due to the diverse challenges for data collection.”

The number of people dying at the border is spiking at the same time border patrol agents in the South are seeing record numbers of people trying to cross into the U.S.

The IOM said mobility restrictions put into place during the pandemic may also be playing a factor by creating a funnel effect, forcing migrants with few options to attempt increasingly dangerous routes, like through the Sonoran Desert or trying to swim across remote stretches of the Rio Grande River.