Twelve civilians were killed in a shelling of a bus in eastern Ukraine Tuesday, which Ukrainian Security Service has classified as a "terror act". The Kiev government and rebels have been accusing each other of being responsible for the incident.

The Russian Foreign Ministry earlier released a statement saying the tragedy proved that all-out and continuous efforts should be made in order to peacefully settle down the ongoing crisis in Ukraine.

Lavrov also stressed at the press conference that the Contact Group meeting is the only platform to reach reconciliation as it directly involves the conflicting sides of Ukraine.

"It is imperative to achieve the full potential (of the contact group meetings) as soon as possible," Lavrov said, adding that the Minsk agreements should be "fully and faithfully" fulfilled.

The foreign ministers of Germany, France, Russia and Ukraine on Monday urged a meeting of the contact group on Ukraine to make progress on implementing the September Minsk peace deal.

Thursday's gathering planned in Astana, the capital of Kazakhstan, seems to be delayed as "more work needs to be done" to get prepared for its success, according to a statement released Tuesday by the Russian Foreign Ministry.