The United States' chief diplomat for Iran has characterized the September missile and drone attack on Saudi Arabia's Aramco oil installations as "an act of war by Iran."

Brian Hook said in an interview aired by CNBC on December 14 that Washington will continue to strengthen its own military forces, as well as those of Saudi Arabia and other countries against probable attacks in the future.

“Because of the Iran nuclear deal, we’ve been accumulating risk of a regional conflict — and what Iran did to Saudi Arabia on September 14 was an act of war,” Hook told CNBC in Qatar on Saturday.

Yemen's Houthis assumed responsibility for the attacks on oil installations in Eastern Saudi Arabia, however, Saudis and U.S. and European officials have continued to blame Tehran for the strike that halved Saudi Arabia's oil output at the time.

Although Iran was named as the perpetrator of the attack, it was not directly accused of an a act of war.

Iran categorically denied the allegations, insisting that its forces were not involved.

UN Chief Antonio Guterres said in a December 10 report to the Security Council that the organization had no independent confirmation the attacks had Iranian origin.

Reports in recent days have said Saudi Arabia is seeking ways to improve ties with Iran.