The first visit to Greece by a Turkish head of state in 65 years has had a tense beginning, with President Recep Tayyip Erdogan and his host exchanging accented comments.
Erdogan said that the 1923 treaty that placed the borders of Turkey after the First World War was not applied fairly.
But Greek President Prokopis Pavlopoulos rejected any change in the Treaty of Lausanne.
Relations between the two NATO members have been uncomfortable for decades.
What is the source? of the tensions?
Many problems. Long-standing disputes over uninhabited islands in the Aegean took both countries to the brink of war in 1996.
They also failed to reach a peace agreement in divided Cyprus: the north of the island was invaded by Turkey in 1974 in response to a military coup backed by Athens.
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Turkey also says that the rights of the Muslim minority of Turkish origin in northeastern Greece are not respected. In Athens, Erdogan said that they were not allowed to choose their own legal expert, or mufti, with the role instead appointed by Greece.
The Turkish government is also unhappy with the decision of the Supreme Court of Greece that blocked the extradition of eight Turkish soldiers who fled to the country after allegedly participating in the failed coup last year.
Meanwhile, Greece complains that Turkey has repeatedly violated its air and naval space.
But the tensions between these neighbors date back to the 1830s when Greece gained its independence from the Ottoman Empire.
What is happening with the visit?
The direct exchange on the Lausanne Treaty occurred on the first of a two-day visit by the Turkish leader, during their joint press conference.
Mr. Erdogan stated that the treatment of Muslims in Greece showed that Athens was not complying with the treaty.
"They are not given the necessary support in terms of investments (…) and there is discrimination," he said, also complaining that some points of the treaty needed clarity.
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Responding to that, Mr. Pavlopoulos, one of Greece's leading legal experts, said: "This treaty, for us, is non-negotiable This treaty has no gaps, it does not need a revision or an update, this treaty is valid as it is. "
The visit, described by Erdogan as "historic", takes place in the middle of a strong security operation, with hundreds of officers deployed.
Both governments hope that the visit will mark a new chapter in bilateral relations, with the signing of joint infrastructure projects, reports Mark Lowen of the BBC in Athens.