Hillary Clinton, US secretary of state, will lend her support to Turkish and Armenian efforts to end one of the most intractable conflicts in the Caucasus when the two countries sign agreements on Saturday to mend diplomatic relations and open their shared border.

Mutual animosity is rooted in the 1915 massacres by Ottoman Turks of up to 1.5m Armenians. Turkey also closed its border with Armenia in 1994 to support its ally Azerbaijan in a conflict with Armenia over the disputed territory of Nagorno-Karabakh.