Armenian and Azerbaijani officials said on Thursday that they had agreed the text of a peace agreement to end nearly four decades of conflict between the South Caucasus countries, a sudden breakthrough in a fitful and often bitter peace process.

But hurdles remain. Azerbaijan also said Armenia’s constitution must “eliminate the claims against the sovereignty and territorial integrity of Azerbaijan,” as a prerequisite to allow for the signing of the peace treaty.

Armenian Prime Minister Nikol Pashinyan and Russian President Vladimir Putin speak at a summit of leaders of nations, which are members of the Commonwealth of Independent States (CIS), at the Kremlin in Moscow,