Russia said on Wednesday it had offered to help mediate demarcation negotiations after Armenia accused Azerbaijan of a border incursion. Armenia has accused Azerbaijan of sending troops across the border last week, highlighting the fragility of a Russian-brokered cease-fire that halted six weeks of fighting between ethnic Armenian and Azeri forces last year. Azerbaijan has denied crossing the frontier and said its forces only defended their side. But Armenia said on Friday that Azerbaijan had failed to fulfil a promise to withdraw troops that had crossed the border. “Russia has offered first of all to provide assistance with the delimitation and demarcation of the border,” Foreign Minister Sergei Lavrov told reporters during a visit to Tajikistan. He said Moscow had proposed setting up a joint Armenian-Azeri commission, with Russia possibly participating as a consultant or mediator. Russian President Vladimir Putin later held separate calls with his Azeri counterpart Ilham Aliyev and Armenian acting Prime Minister Nikol Pashinyan. Putin said Moscow would assist Azerbaijan and Armenia in reaching an agreement, according to a readout of the talks published by the Kremlin. Armen Grigoryan, secretary of the Armenian government’s security council, said demarcation work could not start until Azeri troops had left Armenian territory, TASS news agency reported. However, Armenia’s defense ministry said talks between the Armenian and Azeri defense officials were underway, the Interfax news agency reported. “In the absence of a peaceful settlement within a reasonable timeframe — in the event that Azerbaijan’s military does not return to its original positions without any preconditions — the Armenian armed forces have the right to resolve the issue by other means, including by force,” the ministry said. Moscow helped secure a cease-fire in November after Azeri troops drove ethnic Armenians out of territory they had controlled since the 1990s in and around the Nagorno-Karabakh region. Russia, which has a military base in Armenia, sent peacekeepers to the area last year to help enforce the cease-fire. It has strong ties and a mutual defense pact with Armenia but is also friendly with Azerbaijan.