MEXICO CITY - About 100 Mexican soldiers and immigration agents raided a freight train in southern Mexico early Thursday and detained dozens of Central American migrants riding atop the cars.

Such raids had been rare since the last crackdown on migrants in 2014. But under increasing U.S. pressure to reduce the flow of hundreds of thousands of Central Americans through Mexican territory, Mexico's government has stepped up enforcement.

In a scene filmed by Associated Press journalists, the train rolled to a stop in a rural area, and then soldiers climbed ladders to the top of freight cars shouting, “This is the army, you're surrounded!”

Throngs of migrants sought flee by running along the tops of freight cars, while others clambered down to the ground and headed into the brush.

One soldier was seen wrestling a young, flailing man into a waiting immigration van by the neck. Agents filled three such vehicles with migrants, but hundreds more were apparently able to escape. The train may have been carrying as many as 400 migrants, and only about one in ten appeared to have been caught.

The country's Immigration Institute did not immediately respond to requests for details on the raid in Chiapas state.

The most recent such raid occurred May 1 in the state of Oaxaca. Central Americans have been riding freight trains, collectively known as “La Bestia,” or The Beast, for years.

Previous raids have served to temporarily discourage migrants from hopping aboard the trains, which is technically prohibited but has long been tolerated.