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By Zerin Elci and Jeff Mason
ZURICH (Reuters) - Turkey and Armenia signed a landmark peace accord on Saturday to restore ties and open their shared border after a century of hostility stemming from the World War One mass killing of Armenians by Ottoman forces.
But in an indication of the many pitfalls that lie ahead of its implementation, the ceremony was marred by a three-hour delay due to last-minute disagreements on statements, forcing U.S. Secretary of State Hillary Clinton to engage in intense discussions to salvage a deal.
Turkey's Foreign Minister Ahmet Davutoglu and his Armenian counterpart Edward Nalbandian signed the Swiss-mediated deal in Zurich at a ceremony also attended by European Union foreign policy chief Javier Solana, Russia's Foreign Minister Sergei Lavrov and France's Foreign Minister Bernard Kouchner.
The Turkish and Armenian parliaments must now approve the deal in the face of opposition from nationalists on both sides and a Armenian diaspora which insists Turkey acknowledge the killings of up to 1.5 million Armenians as genocide.
If an agreement comes into effect, it would boost European Union candidate Turkey's diplomatic clout in the volatile South Caucasus, a transit corridor for oil and gas to the West.
Before the deal was inked at the University of Zurich, Clinton returned to her hotel to help smooth over objections with Nalbandian over statements to be read at the ceremony.
She then held a long telephone call with Davutoglu before meeting Nalbandian, with whom she returned to the venue in her motorcade hours later in a night of high drama.
Clinton later promised the United States would do everything it could to build on the "milestone" that Turkey and Armenia had achieved.
Clinton, who declared herself "very pleased" that the protocols had been signed, said both countries had concerns that had delayed the signing ceremony.
Ties between the two neighbours are traumatised by the deportations and mass killings of Armenians by Ottoman Turks, and normalization efforts have been hampered by a decades-old dispute between Turkey's ally Azerbaijan and Armenia over the enclave of Nagorno-Karabakh.
Turkey cut ties and shut its border with Armenia in 1993 in support of Turkic-speaking Azerbaijan which was then fighting a losing battle against Armenian separatists in Karabakh.
Turkish officials told Reuters the two sides had many disagreements over each others' statements, including oblique references to the Karabakh conflict. In the end, neither Davutolgu nor Nalbandian made public statements.
The delay left Solana, Lavrov and Kouchner waiting for more than two hours while the Americans met the Armenians at a nearby hotel in what Reuters witnesses described as tense talks.
Organizers of Saturday's ceremony, which capped months of negotiations, said plans to play Handel's soaring "Royal Fireworks" while the two ministers signed the protocol, were cancelled at the last minute.
A smiling Davutoglu and a stony-faced Nalbandian sat at a table to sign the deal. Once they had put their signatures on several pages, they stood up and shook hands to applause and exchanged hugs and handshakes with the other ministers.
"Your political courage, your relentless efforts and your generous vision has made this agreement possible," Swiss Foreign Minister Micheline Calmy-Rey said.
The European Union welcomed the signing.
"The signature of the protocols confirms the desire of both Turkey and Armenia to turn a page and build a new future. This opens new perspectives for the solution of conflicts, notably in Nagorno-Karabakh," EU External Relations Commissioner Benita Ferrero-Waldner said in a statement.
Although landlocked Armenia stands to make big gains, opening its impoverished economy to trade and investment, Armenia's leader Serzh Sarksyan faces protests at home and from the huge Armenian diaspora, which views the thaw with suspicion.
Armenians demand that Turkey acknowledge the 1915 killings as genocide, a defining element in Armenian national identity.
"Any relations with Turkey cannot call into question that genocide was committed against the Armenian people. This should be recognized and condemned by humankind," Sarksyan said in a televised address before the ceremony.
Under the deal, Turkey and Armenia will set up a commission of international experts to study the events.
Nationalist lawmakers in Turkey have pledged to vote against the deal, and Prime Minister Tayyip Erdogan said earlier this year he would not open the border until Yerevan ended what he called its occupation of Azerbaijan.
(Additional reporting by Katie Reid in Zurich, Hasmik Mkrtchyan in Yerevan and Margarita Antidze in Tbilisi; Writing by Ibon Villelabeitia; editing by Robin Pomeroy)