Police found 210 migrants from Brazil, India, El Salvador and Guatemala inside a trailer on a highway in the southern Mexican state of Chiapas, officials said.

The migrants were discovered on Sunday morning at kilometer 134 of the Ocozocoautla-Las Choapas highway, where a Federal Police checkpoint is located.

The two Mexicans driving the tractor-trailer were arrested and the migrants were handed over to officials at the National Migration Institute, or INM, office in Tuxtla Gutierrez, the capital of Chiapas.

This was the third-largest detention of migrants this year.

Authorities discovered 219 migrants in a tractor-trailer in January and 502 migrants, the majority from Asia and Latin America, were found in two trucks last month.

President Felipe Calderon signed legislation on May 24 aimed at protecting migrants' rights in Mexico.

An estimated 300,000 Central Americans and 400,000 Mexicans undertake the dangerours journey across Mexico each year on their way to the United States.

Central American migrants follow a long route that takes them into Chiapas, which is on the border with Guatemala, walking part of the way or riding aboard freight trains, buses and cargo trucks.

The trek is a dangerous one, with criminals and corrupt Mexican officials preying on the migrants.

The flow of migrants has increased markedly in the northern and northeastern parts of Mexico since U.S. officials increased security along the border in the northwestern part of the country.

The National Human Rights Commission, or CNDH, Mexico's equivalent of an ombudsman's office, recently identified 71 cities in 16 of the country's 32 states that are considered dangerous for Mexican and foreign migrants headed to the United States.

"Kidnappings, abuse, extortion, robberies and sexual attacks on migrants have been documented" in the 71 cities, the CNDH said in a statement.

About 20,000 Central Americans were kidnapped by organized crime groups, which extorted money from them or forced them to join their gangs, the CNDH said in a report released last year.