* Accord would be step towards ending century of hostility
* Some doubts about whether ceremony will take place
(Adds comments from Armenia, details, adds byline)
ANKARA/YEREVAN, Oct 7 (Reuters) - Turkey expects historic accords to normalise ties with Armenia to be signed on Saturday in Switzerland in a step towards ending a century of hostility, senior Turkish government sources said on Wednesday.
But doubts have emerged in diplomatic circles about whether the ceremony would take place because of pressure from the powerful Armenian diaspora, as well as opposition within Armenia and to a certain extent Turkey.
"There are no changes to those plans," a senior Turkish government source, referring to the planned signature of protocols in Zurich on Oct. 10, told Reuters. Another government source, who also declined to be named, agreed.
Armenian Deputy Foreign Minister Arman Kirakossian told Reuters that a decision had not yet been taken on when and where the protocols would be signed but acknowledged they needed to happen shortly as an agreed deadline was approaching.
"The signing ceremony is very important because Armenia has always stated its desire to establish relations without preconditions. And I hope that these protocols will be signed very soon," Kirakossian told Reuters in Yerevan.
Turkey and Armenia have no diplomatic ties because of hostility stemming from the mass killings of Armenians by Ottoman Turks during World War One. Turkey closed its border with Armenia in 1993 in solidarity with fellow Muslim Azerbaijan, then at war with Armenian-backed ethnic Armenians.
Turkey and Armenia agreed on Aug. 31 to sign, within six weeks, two protocols on the establishment of diplomatic ties, opening a common border and for historians to investigate the events surrounding the killings of Armenians in 1915.
But Armenia was taken by surprise when Turkish Prime Minister Tayyip Erdogan announced in New York that the agreements would be signed on Oct. 10.
Turkish Foreign Ministry officials later told reporters each country's foreign minister would attend the ceremony in Zurich.
Armenian President Serzh Sarksyan is on a week-long intercontinental charm offensive to calm concerns in the Armenian diaspora over the historic thaw with Turkey. Diplomatic observers also fear the signing could be disrupted by demands by some Turks for a resolution on the Nagorno-Karabakh dispute.
Armenian nationalists demand that Turkey acknowledge the 1915 killings as genocide and protests have erupted in France and Lebanon. Ankara rejects the term genocide, saying that many people died on both sides of the conflict.
Once the protocols are signed they must be approved by the respective parliaments. This leaves open the possibility that either side delays the approval in case they face unexpected domestic opposition.
Hanging over efforts to re-establish ties is the spectre of one of the bloodiest and most intractable conflicts sparked by the demise of the Soviet Union.
Ethnic Armenian forces, backed by Armenia, fought a war with Azerbaijan in the early 1990s over the mountainous territory of Nagorno-Karabakh, an ethnic Armenian enclave located within Azerbaijan's internationally recognised borders. Some 30,000 people died.
International mediators are trying to put pressure on Armenia to negotiate with Azerbaijan over Karabakh as part of a wider attempt to secure a lasting peace in the region.
Turkey, a close ally of Azerbaijan, has also said ties with Armenia cannot be normalised until there is progress on Nagorno-Karabakh. Armenia insists the two issues are separate.
In the latest diplomatic round, two days before the Swiss ceremony, the leaders of Armenia and Azerbaijan will hold new talks on Karabakh in Moldova's capital Chisinau on Thursday.
Turkish government sources said they did not expect any major breakthrough in Moldova but said the meeting itself would help push a solution to the Nagorno-Karabakh dispute forward.
Additional reporting by Margarita Antidze in Tbilisi; Writing by Paul de Bendern; Editing by Charles Dick
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