Azerbaijan refused to allow international investigations of ceasefire violations around Nagorno-Karabakh shortly after agreeing to the confidence-building measure at an Armenian-Azerbaijani summit in May, Russia’s Foreign Ministry confirmed on Thursday.

The summit was held in Vienna in the presence of U.S. Secretary of State John Kerry, Russian Foreign Minister Sergey Lavrov and French Secretary of State for European Affairs Harlem Desir.

In a joint statement issued after those talks, Kerry, Lavrov and Desir said Presidents Ilham Aliyev and Serzh Sarkisian “agreed to finalize in the shortest possible time an OSCE investigative mechanism.”

Aliyev contradicted the mediators’ statement in late June, shortly after holding follow-up talks with Sarkisian in Saint Petersburg, Russia. He said Baku will allow OSCE investigations of truce violations only if the Armenians and the mediators set “time frames for the liberation of our territories.”

The Russian Foreign Ministry spokeswoman, Maria Zakharova, confirmed that the Vienna summit yielded an agreement on the idea of OSCE investigations which has long been championed by the U.S., Russia and France and backed by Armenia.She said Aliyev walked away from that agreement at the Saint Petersburg summit hosted by Russian President Vladimir Putin.

“The Azerbaijani side insisted that there is no need to investigate armed incidents because the situation in the conflict zone remained stable at that point,” Zakharova told a news briefing in Moscow. “As a result, the theme of the mechanism [for OSCE investigations] was not reflected in the statement [by Aliyev, Sarkisian and Putin] issued after the Saint Petersburg meeting.”

“In our view, the issue of the mechanism issue remains topical,” added the Russian official.

The Armenian government maintains that this and other confidence-building measures proposed by the mediators are essential for reviving substantive negotiations on a peaceful settlement of the Karabakh conflict. It has repeatedly denounced Baku’s reluctance to accept them.