The United States is set to announce on Thursday a $29.4 billion sale of F-15 fighter jets to Saudi Arabia, according to an industry participant familiar with the matter, amid mounting tension with Iran.

The sale covers 84 new Boeing F-15 fighters with advanced radar equipment and digital electronic warfare systems plus upgrades of 70 older F-15s, the industry particpant said.

The deal comes amid rising tensions in the Gulf region, with both the United States and Saudi Arabia worried over Iran's nuclear program. Iran this week repeated threats to close the Strait of Hormuz in response to mounting U.S. and European economic sanctions.

The Obama administration cleared with Congress more than a year ago the potential sale of more than $60 billion of military hardware to Saudi Arabia over 10 to 15 years, including the F-15s, helicopters and related equipment and services.

The Saudi buildup, part of a wider U.S. buildup of its regional friends and allies, could help offset the departure this month of the last U.S. combat troops in Iraq.

(Reporting By Jim Wolf; Editing by Will Dunham)