Israeli Prime Minister Benjamin Netanyahu says he "secretly visited" the United Arab Emirates and met its president during the war with Iran.
Netanyahu's office said the meeting between the Israeli PM and President Sheikh Mohammed bin Zayed had led to a "historic breakthrough".
However shortly afterwards, the UAE foreign ministry said the claims about the visit were "entirely unfounded", and insisted relations between the two countries were not based on "unofficial arrangements".
Iran hit several targets in the Emirates during the conflict, and Tehran has repeatedly criticised the country for what it sees as its closer ties with the US and Israel.
Iran's Foreign Minister Abbas Araghchi said Netanyahu had "publicly revealed what Iran's security services long ago" told the country's leaders.
He added that collusion with Israel was "unforgivable" and those who do so "will be held to account".
In its statement, the UAE foreign ministry denied reports of the alleged visit by Netanyahu or any other Israeli military delegation in the country.
"The UAE reaffirms that its relations with Israel are public and conducted within the framework of the well-known and officially declared Abraham Accords, and are not based on non-transparent or unofficial arrangements."
The Abraham Accords are a set of agreements that established normalised relations between Israel and several Arab countries during President Trump's first term.
Reuters quoted a source as saying the meeting between Netanyahu and the Emirati president took place in Al-Ain, an oasis city near the border with Oman, and lasted several hours.
On Tuesday, the US ambassador to Israel, Mike Huckabee said Israel sent anti-missile batteries from its Iron Dome system to help the UAE combat Iranian attacks.
The Iron Dome is an advanced Israeli air defence system used to intercept and destroy a range of aerial missiles, rockets and drones.
Huckabee said the Iron Dome deployment was the result of an "extraordinary relationship between the UAE and Israel" based on the Abraham Accords.
Israel and the US's war with Iran appears to have deepened those relations - and developed the alliance militarily too.
During the war, Iran launched a series of missiles and drones on the UAE. On 10 May the UAE's Ministry of Defence said that air defence systems had engaged two drones launched from Iran and that the country had engaged a total of 551 ballistic missiles, 29 cruise missiles, and 2,265 since the war broke out in late February, when the US and Israel attacked Iran.
On Monday the Wall Street Journal reported that the UAE had also carried out strikes on Iran, which it had not yet publicly acknowledged, including an attack on a refinery on Iran's Lavan Island in early April.
Earlier on Wednesday Emirati presidential adviser Anwar Gargash said the UAE remained committed to diplomacy but had a right to defend itself.
In his post, Gargash said that the UAE had not sought the war and had worked to avoid it, saying that "Arab-Iranian relations in the Gulf cannot be built on confrontations and conflicts".
A ceasefire has been in place between the US and Iran for about a month.
However Iran has continued to block the Strait of Hormuz in response to US-Israel strikes, prompting a rise in world oil prices. Normally about 20% of the world's oil and liquefied natural gas passes through the strait. The US for its part has been enforcing a blockade of Iranian ports to exert pressure on Tehran to agree to its terms.
On Sunday Iran laid out its demands to end the war and reopen the Strait of Hormuz in a counter-offer sent to the US. Trump rejected the proposal, calling it "totally unacceptable" and a "piece of garbage" and subsequently said the ceasefire was "on massive life support".
Iranian parliamentary speaker Mohammad Ghalibaf responded on X that Iran's armed forces were "ready to respond and to teach a lesson for any aggression".
Additional reporting by Ella Kipling and Tom McArthur
