Yemen’s Iranian-allied Houthi rebels attacked a Saudi airport and military base with a bomb-laden drone Tuesday, an assault acknowledged by the kingdom as Middle East tensions remained high between Tehran and Washington. There were no immediate reports of injuries or damage.

The attack on the Saudi city of Najran came after Iran announced it has quadrupled its uranium-enrichment production capacity, though still at a level far lower than needed for atomic weapons, a year after the U.S. withdrew from Iran’s nuclear deal with world powers.

Underlining the tensions, Iranian President Hassan Rouhani is seeking expanded executive powers to better deal with “economic war” triggered by the Trump’s administration’s renewal and escalation of sanctions targeting the Islamic Republic, the state-run IRNA news agency reported.

“A person or a nation might be under pressure but the Iranian nation will not bow to bullies,” Rouhani vowed in a televised speech Tuesday night.

By increasing production, Iran soon will exceed the stockpile limitations set by the nuclear accord. Tehran has set a July 7 deadline for Europe to put forth new terms for the deal, or it will enrich closer to weapons-grade levels in a Middle East already on edge. The U.S. has deployed bombers and an aircraft carrier to the Persian Gulf over still-unspecified threats from Iran, which is the biggest rival in the region to the U.S.-allied Saudi Arabia.

Before a briefing on the situation to Congress , acting Defense Secretary Patrick Shanahan suggested the U.S. military response to Iranian threats has already had an effect. He said U.S. military moves have given Iran “time to recalculate” and as a result the potential for attacks on Americans is “on hold,” although the threat has not gone away.

In the drone attack, the Houthis’ Al-Masirah satellite news channel said they targeted the airport in Najran with a Qasef-2K drone, striking an “arms depot.” Najran, 840 kilometers (525 miles) southwest of Riyadh, lies on the Saudi-Yemen border and has repeatedly been targeted by the Houthis.

A statement on the state-run Saudi Press Agency quoted Saudi-led coalition spokesman Col. Turki al-Maliki as saying the Houthis “had tried to target” a civilian site in Najran, without elaborating.

Al-Maliki warned there would be a “strong deterrent” to such attacks and described the Houthis as the “terrorist militias of Iran.” Similar Houthi attacks have sparked Saudi-led airstrikes on Yemen, which have been widely criticized internationally for killing civilians.

Civilian airports across the Middle East often host military bases.

The New York Times reported last year that American intelligence analysts were based in Najran, assisting the Saudis and a deployment of U.S. Army Green Berets on the border. Lt. Col. Earl Brown, a spokesman for U.S. Central Command, said there were “no U.S. personnel involved nor present at Najran” at the time of the attack.

Last week, the Houthis launched a coordinated drone attack on a Saudi oil pipeline. Earlier this month, officials in the United Arab Emirates alleged that four oil tankers were sabotaged and U.S. diplomats relayed a warning that commercial airlines could be misidentified by Iran and attacked.