SANTIAGO, Jan 26 (Reuters) - Chile's environmental regulator accused a major hydroelectric power facility operated by U.S.-based AES of violations, largely related to a failure to build required infrastructure but also charges it skirted its ecological obligations.

Environment regulator SMA outlined four charges covering AES' $3.5 billion Alto Maipo project in a statement on Thursday, which also accuse it of engaging in work in a protected paleontological area plus unlawful moving of fauna.

Alto Maipo, located southeast of the capital Santiago, features two power plants and an extensive network of tunnels that extend deep under the Andes Mountains. It has been mired in controversy dating back several years, including fierce opposition from local communities who complain the facilities harm their access to water.

An audit showed that the company's local unit AES Andes failed to build a "complementary" water outlet for irrigation for a canal set out in previously agreed to deal with local communities, SMA Superintendent Marie Claude Plumer said in the statement.

AES Andes did not immediately respond to a request for comment.

The violations could lead to a fine of around $18.5 million, the closure of the plants or the termination of its environmental permit.

AES Andes sells electricity to Chile as well as Colombia and Argentina.

It has 10 working days to present a compliance plan and 15 working days to submit its response, according to the regulator. (Reporting by Fabián Andrés Cambero; Editing by David Gregorio)