* U.S. treasury secretary accompanies Israeli delegation
* Israel and Bahrain last month agreed on formal ties
* U.S. also brokered Israel-United Arab Emirates deal (Updates with signing of communique, quotes throughout)
By Dan Williams
MANAMA, Oct 18 (Reuters) - Bahrain and Israel signed a joint communique to formalise nascent ties during a visit by an Israeli and U.S. delegation to Manama on Sunday to broaden cooperation that Washington has promoted as an anti-Iran bulwark and potential economic bonanza.
Bahrain followed the United Arab Emirates in agreeing last month to normalise ties with Israel, stunning Palestinians who had demanded statehood before any such regional rapprochement.
The breakthrough, overseen by U.S. President Donald Trump, is a foreign policy flourish ahead of his bid for re-election next month. For the U.S. allies, it is a chance to close ranks on Iran more overtly.
The Israeli delegation, which flew on an El Al Israel Airlines charter flight from Ben Gurion airport in Tel Aviv, was accompanied by U.S. Treasury Secretary Steve Mnuchin.
"It was indeed an historic visit, to start opening relations between both countries," Bahraini Foreign Minister Abdullatif Al-Zayani said after the signing ceremony with Israel's Foreign Ministry director general Alon Ushpiz and National Security Adviser Meir Ben-Shabbat.
Al-Zayani touched elbows with Ben-Shabbat, who described the step as a "promising beginning" and said the Israeli delegation was accepted "with open arms, with warmth and cordiality."
Israel and Bahrain, host to the U.S. Navy's Fifth Fleet, signed a "Declaration of Peace, Cooperation, and Constructive Diplomatic and Friendly Relations" at a White House ceremony on Sept. 15, a document that fell short of a formal treaty.
The accord has drawn anger among Bahrainis at home and abroad. The government of Bahrain, where a Sunni Muslim minority rules a Shi'ite majority population, has said the deal protects its interests from Iran.
Al-Zayani said engagement and cooperation were the most effective and sustainable way of bringing about genuine and lasting peace in the region, and said his country supported resolving the Israeli-Palestinian conflict through dialogue.
JUST THE BEGINNING
Mnuchin described the accord as an important step in regional stability and "just the beginning of the work that is going forward".
"I think the opportunity is way beyond just investments," Mnuchin earlier told reporters on the El Al flight. "It's in technology, building various different businesses - and in the case of Bahrain as well, really expanding the opportunities for them quite, quite, quite dramatically."
The ceremony also saw the signing of several memoranda of understanding. They cover trade, air services, telecommunications, finance, banking and agriculture, according to a list provided by a Bahraini official.
Houda Nounoo, a Bahraini diplomat, told reporters the Gulf state planned to formally reopen Manama's old synagogue, which has a Jewish community of 34 people, for the Purim festival on Feb. 25.
Ben-Shabbat, speaking in Arabic at an arrival ceremony at Manama airport, said Israel looked forward to hosting a Bahraini delegation in Israel soon.
The El Al flight flew over Saudi Arabia, an accommodation by the Gulf's powerhouse, which has so far resisted U.S. appeals to normalise ties with Israel.
Mnuchin and the other U.S. officials travel on Monday to the UAE, where the accord with Israel has uncorked bilateral commerce. On Tuesday the U.S. dignitaries will join the UAE's first delegation to Israel.
Israel and the UAE will sign a deal on Tuesday to allow 28 weekly commercial flights between Tel Aviv's Ben Gurion airport, Dubai and Abu Dhabi, Israel's Transportation Ministry said on Sunday. (Additional reporting by Aziz El Yaakoubi, Ghaida Ghantous, Jeffrey Heller, Tova Cohen and Ari Rabinovitch Editing by Rami Ayyub, David Goodman and Alexandra Hudson)
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