Turkey and Armenia signed a landmark agreement to establish diplomatic relations and open their sealed border after a century of enmity, as US Secretary of State Hillary Clinton helped the two sides clear a last-minute snag.
The contentious issue of whether the killing of up to 1.5 million Armenians during the final days of the Ottoman Empire amounted to genocide is only hinted at in the agreement.
"There were several times when I said to all of the parties involved that this is too important," Mrs Clinton said.
"This has to be seen through. We have come too far. All of the work that has gone into the protocols should not be walked away from."
The Turkish and Armenian foreign ministers signed the accord in the Swiss city of Zurich after a dispute over the final statements they would make.
In the end, the signing took place about three hours later than scheduled and there were no spoken statements.
Mrs Clinton and mediators from Switzerland intervened to help broker a solution, US officials said.
Better ties between Turkey, a regional heavyweight, and poor, landlocked Armenia have been a priority for President Barack Obama, and Mrs Clinton had flown to Switzerland to witness the signing, not help close the deal.
Mrs Clinton told reporters travelling later on the plane with her to London that both sides had problems with the other's prepared statement and that the Armenian foreign minister had to call his president several times.
She said it became important just to approve the accord and not have the sides make speeches that could be interpreted as putting legal conditions on the document. She told each country that could be done later, "but let the protocols be the statement because that was what we were there to sign."
The accord is expected to win ratification from both nations' parliaments and could lead to a reopening of their border within two months. It has been closed for 16 years.
But nationalists on both sides are still seeking to derail implementation of the deal.
UN Secretary-General Ban Ki-moon called the signing a "historic decision" that "constitutes a milestone toward the establishment of good neighbourly relations," spokeswoman Michele Montas said in New York.