Russia is extremely concerned about the worsening situation on Armenia's border with Azerbaijan and calls on the sides to show restraint and observe the ceasefire regime, Russian presidential aide for international affairs Yuri Ushakov said, RIA Novosti reported.

"We, of course, express extreme concern in connection with the aggravation of the situation in certain areas of the Armenian-Azerbaijani border," he told reporters. Ushakov recalled that Russian President Vladimir Putin received a phone call overnight from Armenian Prime Minister Nikol Pashinyan.

"We call on both Azerbaijan and Armenia to show restraint, strictly observe the ceasefire and generally comply with the well-known trilateral statements of the leaders of Russia, Azerbaijan and Armenia," he said.