The United States announced on Tuesday that weapons deliveries to Arab allies who are fighting Iranian-backed rebels in Yemen would be expedited.

In a visit to the Saudi capital Riyadh, Deputy Secretary of State Antony Blinken praised the kingdom for sending a “strong message” to the Houthi rebels in Yemen.

Besides speeding up arms supplies, the United States will also boost intelligence sharing and establish a joint coordination center for the operation in Saudi Arabia, Blinken said.

Thirteen days of bombing by military jets from Saudi Arabia and other Sunni states in the Middle East appear to have only slowed the Houthis’ advance. The airstrikes as well as several airdrops of weapons have enabled fighters loyal to Yemen’s internationally-recognized president, Abd Rabbuh Mansur al-Hadi, to stop the northern rebels taking over the port city of Aden. But the Houthis remain in control of much of the west of the country.

In the north, Houthis near Hudaydah on the Red Sea coast were also attacked. Egyptian and Saudi navy ships are involved in the campaign.

Saudi Arabia intervened in the conflict to stop a group it sees as a proxy of its regional nemesis, Iran.

The Houthis, fighting alongside troops loyal to Hadi’s predecessor, Ali Abdullah Saleh, stormed the capital, Sana’a, last year and forced Hadi to seek refuge in Aden in February. He later fled to Saudi Arabia.

Despite the involvement of its allies and the attacks it previously carried out against suspected terrorists in Yemen with unmanned drone aircraft, America has remained on the sidelines of the latest conflict.

The Saudi-led intervention came as the United States were on the verge of doing a nuclear deal with Iran. Negotiations in Switzerland between the Shia state and world powers produced a tentative accord last week under which Iran should not be able to develop nuclear weapons.

Arab countries fear the United States may acquiesce in recent Iranian strategic gains in the Levant in order to get a long-term nuclear agreement or even pursue broader rapprochement with a country that severed its ties with the West in 1979 when it deposed the monarchy.

Iran and Saudi Arabia are locked in a struggle for regional hegemony. The powers back opposing sides in Yemen as well as in Syria’s civil war. Iran supports the regime of President Bashar al-Assad there while Saudi Arabia has armed and financed the largely Sunni uprising against him.

Although Iran has thrown its support behind the Houthis, it did not instigate their rebellion.

Until the middle of last year, the Houthi campaign was little more than a turf war against tribal opponents in the highlands of northern Yemen. Only recently, with the support of Saleh loyalists, did they take the fight to Hadi’s government after he had proposed to federalize the country.