LONDON — Iran has told the United Nations nuclear supervisory body that it plans to install more sophisticated equipment at its principal nuclear enrichment plant, a diplomat said Thursday, enabling it to greatly accelerate processing of uranium in a move likely to worry the United States, Israel and the West.

The diplomat, based in Vienna, where the International Atomic Energy Agency has its headquarters, cited a letter from Iranian officials to the agency saying that Iran wants to upgrade its main enrichment plant at Natanz. The upgrade could speed up enrichment by as much as two or three times, the diplomat said on the condition of anonymity, in light of the confidential nature of the Iranian note.

The United States and its allies accuse Tehran of seeking the technology for nuclear weapons, but Iran says it wants to use enriched uranium purely for civilian and peaceful purposes.

The disclosure came at a time of high regional tension, a day after American officials said Israeli warplanes struck deep inside Syrian territory. The American officials said they believed the target was a convoy carrying sophisticated antiaircraft weaponry on the outskirts of the Syrian capital, Damascus, that had been intended for Hezbollah in Lebanon.