DUBAI, U.A.E.: Saudi warplanes have carried out heavy airstrikes in Yemen while Houthi fighters have launched drones and missiles at Saudi cities, the Iran-backed group said on September 16. The attacks followed a rapid Houthi advance that has increased Iran's influence in another part of the Middle East war.

The conflict has also raised concerns in Washington. The United States tightened its travel warning for Saudi Arabia and barred government employees from traveling within 20 miles of the Yemen border.

Since last week, the Houthis have quickly captured towns along Yemen's Red Sea coast and taken control of islands near the Bab el-Mandeb Strait. The group released video showing its fighters capturing armored vehicles from Saudi-backed forces. The footage also showed warplanes flying overhead and large explosions rising from desert areas.

Houthi military spokesman Yahya Saree said the group had launched new drone and missile attacks on the Saudi Red Sea oil port of Yanbu and an airbase at Khamis Mushait in southern Saudi Arabia. He did not say when the attacks took place.

Both cities were among several Saudi locations that issued security alerts on September 15, although there were no similar announcements on September 16. Saudi officials and state oil company Aramco did not immediately respond to requests for comment.

Saree also claimed that Houthi forces had shot down a Saudi F-15 fighter jet, but no immediate evidence was provided to support the claim.

He said Saudi Arabia had carried out as many as 450 airstrikes in Yemen during the week. Officials in the Saudi-backed Yemeni government have confirmed that their forces, together with Saudi forces, were carrying out airstrikes against Houthi positions. Riyadh itself has not officially confirmed the attacks.

The Houthis have repeatedly fired missiles and drones towards Saudi Arabia over the past week, triggering alerts in cities in the south and west. An attack blamed on Iran-aligned fighters in Iraq last week also knocked out Saudi Arabia's East-West Pipeline, a major route for moving oil exports around the Strait of Hormuz blockade.

Saudi Arabia said its air defenses destroyed a Houthi drone south of Mecca before it entered restricted airspace over the holy city. Saudi authorities said the incident crossed a "red line" because it threatened Islamic holy sites. Houthi spokesman Saree denied that Mecca was the target and accused Saudi Arabia of using the incident for propaganda.

Reuters sources said U.S. officials met the Houthis in Oman over the weekend. During the meeting, the Houthis reportedly said they did not intend to attack American ships and remained committed to a ceasefire agreed with Washington last year.

Global Energy Supply at Risk

The expansion of the war into Yemen could further worsen a global energy shortage caused by the six-month-old U.S.-Israeli war with Iran. That conflict has already disrupted shipping through the Strait of Hormuz.

Brent crude oil was trading at about US$108 a barrel on September 16, close to its highest level since May. In the United States, the average retail price of diesel rose above $6.30 a gallon, reaching another record high.

Traders said a long shutdown of Saudi Arabia's East-West Pipeline could remove up to four percent of global oil supply from the market. Saudi Arabia has not said when the pipeline will restart. However, U.S. Energy Secretary Chris Wright told CNBC on September 15 that crude oil should begin flowing through the pipeline within days.

The situation presents a difficult choice for U.S. President Donald Trump. Continued Houthi advances could add to pressure on global energy supplies, while greater U.S. military support for Saudi Arabia could expand the American intervention into another part of the conflict.