By Jonathan Spicer

ISTANBUL, March 25 (Reuters) - Turkey "is playing a role passing messages" between Iran and the U.S. to encourage de-escalation and direct negotiations, Harun Armagan, vice chair of foreign affairs for President Tayyip Erdogan's ruling party, told Reuters on Wednesday.

He did not elaborate on the messages but said they were also being conveyed to Gulf nations, which have been caught up in the widening regional war sparked by the U.S.-Israeli attacks on Iran.

Iran's military on Wednesday rejected President Donald Trump's assertion that the United States was in negotiations to end the war.

NATO member Turkey had sought to mediate U.S.-Iran talks before the attacks began nearly a month ago and has repeatedly called for an immediate halt to hostilities. Erdogan has said it would continue working with all its resources to secure peace.

Foreign Minister Hakan Fidan has said Ankara was conveying "friendly" advice to Tehran to avoid widening the war, and that he was also in touch with Washington to understand where the sides stood.

On Sunday, a Turkish diplomatic source said Fidan had spoken with U.S. officials and also with Iranian Foreign Minister Abbas Araqchi, among others, to discuss possible steps to end the war.

Three Iranian missiles bound for neighbouring Turkey have been downed by NATO air defences since the war began.

(Reporting by Jonathan Spicer; Editing by Alex Richardson)