El Paso, Texas - More than 4,000 archaeological artifacts looted from Mexico and seized in the US, have been returned to Mexican authorities in what experts say is one of the largest such repatriations between the two countries.

The returned items date from before European explorers landed in North America are comprised of items from hunter-gatherers in pre-Columbian northern Mexico. Some of the items include stones used to grind corn, statues, figurines, and copper hatchets, said Pedro Sanchez, president of the National Archaeological Council of Mexico.

US Immigration and Customs Enforcement agents seized the relics in El Paso, Phoenix, Chicago, Denver, San Diego, and San Antonio, though most of the artifacts — including items traced to a 2008 theft from a museum in Mexico — turned up in Fort Stockton, a Texas town about 230 miles southeast of El Paso.

More than two dozen pieces of pottery were seized in Kalispell, Montana, where Homeland Security agents discovered that a consignor had paid Mexican Indians to loot items from burial sites deep in the Mexican Copper Canyon in Chihuahua, Mexico, authorities said.

Although most of the items turned over are arrowheads, several items are of "incalculable archaeological value," Sanchez told the Associated Press. He said it was the biggest archaeological repatriation in terms of the number of items that the US has ever made to Mexico.

US officials displayed the relics at the Mexican Consulate in El Paso before handing them over during a ceremony Thursday. The artifacts will eventually be taken to the National Institute of Anthropology and History in Mexico City, where they will be studied, cataloged and distributed to museums across Mexico.

Most of the items were uncovered during a string of seizures in West Texas in 2009, following a tip about relics illegally entering the United States at a border crossing in Presidio, Texas.

Homeland Security special agent Dennis Ulrich said authorities executing a search warrant in Fort Stockton found the largest portion of the cache. Further investigation revealed that the two men behind the smuggling were also involved in drug trafficking from Mexico to the United States, he said.

Sanchez said some of the relics found in Fort Stockton were stolen from a private collection at the Cuatro Cienagas museum in the Mexican state of Coahuila. The items also include arrows, hunting bows and even extremely well conserved textile items such as sandals and pieces of baskets.