The tense exchange took place in front of allied foreign ministers and was symptomatic of the mutual distrust between the US and many of its European allies over the war in Ukraine, Axios reported.

During a discussion on Ukraine, Kallas challenged Rubio over the US failure to escalate pressure on Russia. She reminded him of a pledge he had made at a G7 meeting a year earlier — that Washington would take more decisive action against Moscow if Russia continued to obstruct American peace efforts.

"A year has passed, and Russia hasn't moved. When will you run out of patience?" Kallas said, according to the sources.

Rubio's response was sharp. "We are doing everything in our power to end the war. If you think you can do it better, go ahead. We'll step back," he said, raising his voice, the sources told Axios.

He added that the US was trying to negotiate with both sides while only supplying one of them — Ukraine — with weapons, intelligence, and other support.

Several European ministers in the room intervened after the exchange, telling Rubio they still wanted Washington to continue its diplomatic engagement with both Russia and Ukraine, one source said. At the end of the meeting, Rubio and Kallas briefly stepped aside to try to ease the tension, two sources said.

Rubio's public denial

Speaking informally to reporters after the G7 session, Rubio denied any tension had occurred.

"These meetings are often about thanking America for the role we've played... and expressing gratitude for the mediating role we've tried to play in this war between Russia and Ukraine. Nobody there is screaming, raising their voice, or saying anything negative," he said.

Zelenskyy dispute

Following the ministerial talks, Rubio also rejected Ukrainian President Volodymyr Zelenskyy's claim that Washington was prepared to offer Ukraine security guarantees only on condition of its withdrawal from Donetsk and Luhansk oblasts.

Zelenskyy had stated that the US was offering Kyiv security guarantees only in exchange for pulling Ukrainian forces from the unoccupied part of Donbas. Rubio called that characterisation false.

The Financial Times reported in January that US security guarantees for Ukraine would be contingent on Kyiv's prior agreement to withdraw its troops from the unoccupied part of Donbas.

Ukrainian President Volodymyr Zelenskyy met with UAE President Mohammed bin Zayed Al Nahyan during his Gulf tour, announcing a bilateral agreement on security and defense cooperation, Zelenskyy reported on social media.

The UAE president thanked Ukraine for the work of its team already operating in the country, according to Zelenskyy's post. The two leaders discussed the security situation in the region, Iranian strikes, and the potential blockade of the Strait of Hormuz.

"For Ukraine, this is also fundamentally important: terror must not prevail anywhere in the world. There must be enough protection everywhere. Therefore, we are open to joint work, which in the strategic perspective will definitely strengthen our peoples and the protection of life in our states," Zelenskyy wrote.

He thanked the UAE side for its "readiness to work together" and confirmed the two countries had reached an agreement. "Teams are finalizing the details," he added.

Ukrainian troops on the ground

Zelenskyy also met with Ukrainian military personnel who have been working in the UAE for several weeks, he said, "to provide assistance in protecting lives." Ukrainian experts have already held meetings with representatives of the UAE Security and Defense Forces.

"There is already a clear understanding of how the sky protection system and critical infrastructure in the Emirates can be strengthened by integrating Ukrainian experience. We are talking about comprehensive solutions that have proven their effectiveness," Zelenskyy said.

Among the Ukrainian military personnel shown in footage from the visit was Tymur Khromaiev, a serviceman of the 112th Separate Territorial Defense Brigade specializing in electronic warfare and drones. Volunteer Serhii Prytula previously stated that Khromaiev "was involved in developing one very cool system that is now being scaled" as part of Prytula's Foundation "Anti-Shahed" project. Khromaiev is also the husband of Ukrainian TV presenter Maria Yefrosinina.

Saudi Arabia visit

The UAE meeting followed Zelenskyy's visit to Saudi Arabia, where he met with Crown Prince Mohammed bin Salman Al Saud and Ukrainian military experts working in the kingdom. The two countries' defense ministries signed a defense cooperation agreement covering technological cooperation and investments.

Zelenskyy said the document "lays the foundation for further contracts, technological cooperation and investments and strengthens Ukraine's international role as a security donor."

Earlier, Zelenskyy disclosed that Saudi Arabia, Qatar, the UAE, Bahrain, Jordan, Kuwait, and the United States had all approached Ukraine for expertise in air defense.