By Ayesha Rascoe

WASHINGTON (Reuters) - The U.S. offshore drilling regulator on Wednesday formally issued sanctions against BP and the major contractors for the 2010 explosion on the Deepwater Horizon rig that killed 11 workers and unleashed more than 4 million barrels of oil into the Gulf of Mexico.

The newly formed Bureau of Safety and Environmental Enforcement filed 15 "incidents of non-compliance" to the companies. It did not release details of how much the companies may face in fines.

By law, the companies face fines of up to $35,000 a day, per incident for the violations.

The infractions uncovered during the federal probe of the accident were outlined in the Interior Department's final report on the disaster, released last month.

BP, owner of the ruptured Macondo well, received the lion's share of the sanctions, with seven notices for violations ranging from failure to protect health and property to failing to keep well under control at all times.

In a first for the department, BP's contractors Transocean, which owned the Deepwater Horizon rig, and Halliburton, which carried out cementing on the well, also face sanctions.

The contractors each received four notices of violations.

Traditionally, the department has only gone after a well's operators for rule infractions. But after last year's spill, the department has asserted its has authority to regulate contractors.

The decision to sanction Transocean and Halliburton reflects the "severity of the incident, the findings of the joint investigation, as well as Secretary Ken Salazar and Director (Michael) Bromwich's commitment to holding all parties accountable," the regulator said in a statement.

(Editing by David Gregorio)