Gunmen kidnapped a group of migrants in Medias Aguas, a city in the eastern Mexican state of Veracruz, a spokesman for the Hermanos en el Camino shelter in Ciudad Ixtepec told Efe.

"We don't have much to go on right now," Hermanos en el Camino spokesman Alberto Donis said, adding that eyewitnesses reported the kidnapping to the shelter.

More than 200 migrants were riding on a freight train from Ixtepec to Veracruz last Friday when the train suddenly stopped in Medias Aguas, Donis said.

About a dozen armed people riding in four SUVs went over to the tracks and started kidnapping migrants, Donis said.

"Get off you sons of whores, get off fast and get in the trucks," eyewitnesses quoted the gunmen as saying.

The kidnapping victims included women and children, eyewitnesses said.

"Some of them ran into the bushes to save their lives and others who were unable to escape were captured by these people and later taken away in the SUVs to an unknown destination," the shelter said in a statement released on Sunday.

Hermanos en el Camino is run by the Rev. Alejandro Solalinde, a prominent defender of migrants' rights.

"The number of migrants kidnapped has not been determined, but it was several, according to the testimony of some of those who escaped and reached us," the shelter said.

"We are awaiting the arrival of the others who escaped or those who were released after paying ransom," Donis said.

Medias Aguas is located about 80 kilometers (50 miles) southwest of Coatzacoalcos and some 120 kilometers (75 miles) north of Ciudad Ixtepec.

The incident is unfortunate because the situation had been improving in the area and no mass kidnappings had occurred recently, Donis said.

Gunmen working for Los Zetas, considered Mexico's most violent drug cartel, may have staged the mass kidnapping, migrant rights activists said.

At least 11,333 migrants, the majority of them from Central America, were kidnapped in Mexico between April and September 2010, the National Human Rights Commission, or CNDH, said in a report released in February.

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 state, 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 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.