By Parisa Hafezi, Samia Nakhoul and Andrew Mills

DUBAI (Reuters) -Tehran has asked Qatar, Saudi Arabia and Oman to press U.S. President Donald Trump to use his influence on Israel to agree to an immediate ceasefire with Iran in return for Iranian flexibility in nuclear negotiations, two Iranian and three regional sources told Reuters on Monday. 

Gulf leaders and their top diplomats worked the phones all weekend, speaking to each other, to Tehran, Washington and beyond in an effort to prevent a widening of the biggest ever confrontation between longstanding enemies Israel and Iran.

Iran is willing to be flexible in the nuclear talks if a ceasefire is reached, one of the Iranian sources said.

The Gulf states are deeply concerned the conflict will spin out of control, a Gulf source close to government officials told Reuters. 

Qatar, Oman and Saudi Arabia have all appealed to Washington to press Israel to agree to a ceasefire and to resume talks with Tehran towards a nuclear deal, the Gulf source said. 

A regional source and an official briefed on Iran's communications with the Gulf said Tehran had reached out to Qatar and Oman to mediate a return to nuclear talks, but insisted that a ceasefire with Israel be put in place first. 

Iran made clear to Oman and Qatar that it would not negotiate while it is under attack and will only begin serious negotiations once it has finished responding to Israeli strikes, the official said.

Iran's foreign ministry was not immediately available to respond to Reuters' request for comment. Qatar's foreign ministry, Oman's ministry of information, Saudi Arabia's international media office, the White House and the U.S. State Department did not immediately respond to requests for comment.

Israeli Prime Minister Benjamin Netanyahu's office did not respond to a request for comment.

When asked if a diplomatic mechanism was being worked out to end the campaign, Israeli National Security Adviser Tzachi Hanegbi told Army Radio on Monday: "It is a little early for that. You don't go to war and look to end it three days later."

Israel launched a surprise attack on Iran on Friday morning that wiped out the top echelon of Iran's military command and damaged its nuclear sites, and says the campaign will continue to escalate with the stated goal of eliminating Tehran's ability to develop a nuclear weapon. 

Iran insists its nuclear programme is civilian, not military. 

PUSH TO RESUME TALKS

Mediator Oman is drafting a ceasefire proposal designed to restart talks between the U.S. and Iran on Iran's nuclear programme, another regional source said.

A sixth round of US-Iran that had been planned in Muscat last Sunday was cancelled a day after Israel's surprise attacks on Friday. 

The Omani draft calls on the U.S. to accept Iran's suspension of all nuclear enrichment for a minimum of one to three years while allowing firm inspections by the International Atomic Energy Agency (IAEA), the regional sources told Reuters. 

The proposed deal would aim to build trust so Iran could enrich uranium up to a purity of 3.67% and allow an international uranium consortium to take part in Iran's program. 

That proposal overlaps with what one of the Iranian sources said Tehran could accept if Israel agreed to an immediate ceasefire: a one-year suspension of nuclear enrichment, full access to IAEA inspectors and confidence-building measures. 

In return, the Iranian source said Iran expects the U.S. to recognise its right to a peaceful nuclear program and to lift sanctions. 

The two Iranian sources said that Tehran had also asked Turkey to appeal to Trump and that Russian President Vladimir Putin had agreed to speak both to Trump and to Israeli Prime Minister Benjamin Netanyahu. It is unclear if Russia would play a broader diplomatic role. 

The Turkish president's office did not immediately respond to a request for comment.

Iran has vowed to "open the gates of hell" in retaliation for Israeli attacks, but the two Iranian sources said that Tehran had also signaled its willingness to halt its strikes if Israel stopped attacking. 

Tehran is serious about pursuing a ceasefire because of fears the war could spread across the region with consequences that could last for decades, one of the Iranian sources said. 

(Reporting by Parisa Hafezi and Samia Nakhoul in Dubai and Andrew Mills in Doha; Additional reporting by Pesha Magid in Riyadh, Maayan Lubell in Jerusalem, Jonathan Spicer in Istanbul and Gram Slattery in Washington; Writing by Andrew Mills; Editing by Aidan Lewis)