Ukraine is awaiting White House approval for a major drone production agreement proposed by Kyiv last year, Ukrainian President Volodymyr Zelenskyy said Thursday, as countries scramble to modernize their air defenses after the Iran war exposed shortcomings.

The proposed U.S.-Ukraine deal would cover various types of drones and air defenses that operate as a single system capable of protecting against swarms of hundreds or even thousands of Iranian-designed Shahed drones and missiles, Zelenskyy said in a message on social media.

"We have not yet had the opportunity to sign this document," he said.

Russia has fired tens of thousands of Iranian-designed Shahed drones at Ukraine since it invaded its neighbor just over four years ago. It launched a swarm of more than 800 drones and decoys in its biggest nighttime barrage. Iran has responded to joint U.S.-Israeli strikes by firing the same type of drones at targets in the Middle East.

Ukraine has pioneered the development of cut-price drone killers, some of which cost a few thousand dollars, that have rewritten the air defense rule book.

The conflict unfolding in the Middle East might prompt American officials to sign the drone production proposal, Zelenskyy said.

Ukraine is keen to lock in future foreign support for its ongoing effort to thwart Russia's invasion, and drone production agreements could bring Kyiv some diplomatic leverage in negotiations with Moscow.

U.S.-mediated talks seeking to stop Europe's biggest conflict since World War II are on hold due to the Iran war.

Zelenskyy arrived in NATO member Romania on Thursday, a day before he visits French President Emmanuel Macron in Paris, as new research indicated Russian oil revenue that helps drive its invasion of Ukraine has risen since the Iran war began.

Russia's daily revenue from oil sales during the Middle East conflict, which has brought a sharp increase in the price of crude, has been on average 14% higher than in February, according to the nonprofit Centre for Research on Energy and Clean Air. Oil revenue is crucial for Moscow's war effort.

Macron's office said his talks with the Ukrainian leader will focus on efforts to counter Russia's so-called shadow fleet of tankers that are shipping oil in violation of international sanctions but are hard to stop.

Zelenskyy was to meet in Bucharest with Romanian President Nicu or Dan, Prime Minister Ilie Bolojan and visit a training center for Ukraine's F-16 pilots.

Ukraine has exported a significant amount of its grain through Romania during the war, and Bucharest has provided energy support to Kyiv as Moscow's forces blast Ukraine's power grid.