By Colin Packham

SYDNEY (Reuters) - French President Emmanuel Macron on Wednesday said he did not know whether U.S. President Donald Trump would stick to the 2015 Iran nuclear deal that many in the West see as the best hope of preventing Tehran from getting a nuclear bomb.

Macron, followed by German Chancellor Angela Merkel, visited Washington last week in the hope of persuading Trump not to reimpose sanctions on Iran before a May 12 deadline and imperil the 2015 deal but the White House has sounded unconvinced.

Under the accord, Tehran agreed to limit its nuclear program in return for relief from U.S. and other economic sanctions. The deal was struck by Britain, China, France, Germany, Russia, the United States and Iran.

"I don't know what the U.S. president will decide on the 12th May," Macron told reporters in Sydney after meeting Prime Minister Malcolm Turnbull on a rare visit by a French president to Australia.

On Tuesday, White House press secretary Sarah Sanders said the agreement on limiting Iran's development of nuclear weapons was reached under false pretences because the country's nuclear program was more advanced than it indicated at the time.

Macron said he had pushed the idea of a much broader Iran agreement with Trump, which was received "very positively".

"I just want to say whatever the decision will be, we will have to prepare such a broader negotiation and a broader deal because I think nobody wants a war in the region, and nobody wants an escalation in terms of tension in the region," Macron added.

Macron's visit to Australia, only the second by a French president, comes amid heightened tensions in the Pacific where France has numerous interests.

France has five island territories spanning the Indo-Pacific: Reunion and Mayotte in the Indian Ocean, and Noumea, Wallis and Futuna and French Polynesia in the Pacific.

Australia and New Zealand have each separately warned China is seeking to exert influence in the Pacific through its international aid program, an allegation Beijing denies.

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While not naming China, Macron said France will increase its influence in the region to ensure "rules-based development".

"It's to preserve necessary balances in the region. And it's important with this - precisely this new context not to have any hegemony in the region."

Macron, speaking at Australian prime minister's official residence in Sydney where he thanked Turnbull and his "delicious wife" for their welcome,, also condemned rioting by anarchists at Tuesday's annual May Day rally in Paris.

Police arrested more than 200 people in the French capital after anarchists hijacked the rally by labor unions against Macron's economic reforms.

(Reporting by Colin Packham and Jane Wardell; Editing by Nick Macfie)