EL PASO, Texas (AP) — A large number of migrants in Mexico who were “posing a potential threat to make a mass entry” into the United States were prevented from cross a bridge leading to El Paso, Texas, a U.S. Customs and Border Protection spokesperson said.

Physical barriers were put up to restrict entry at the Paso Del Norte International Bridge on Sunday afternoon, spokesperson Roger Maier said in a statement.

Barricades also were used for a short time Sunday afternoon at an El Paso crossing at the Bridge of Americas and at one in Stanton, Maier said.

Traffic was reopened and flowing in both directions as of Sunday evening, he said.

Maier said the Office of Field Operations Special Response Team and U.S. Border Patrol agents assisted Customs officers.

It wasn’t immediately known what caused the attempted mass crossing.

A message seeking comment was left with the mayor’s office in El Paso.