MOSCOW, Jan. 14 -- Russia warned Kiev authorities against attempts to revert to use of force to resolve the Ukraine crisis, Foreign Minister Sergei Lavrov said Wednesday.

"We are very worried ...that the ceasefire regime, which seems to have just started to be established, is being violated. Shellings occurred regularly and widely in the past few days," an online statement released by the Russian Foreign Ministry quoted Lavrov as saying.

"We warn our Ukrainian colleagues against attempts to return to force scenarios. This conflict could be resolved only by direct dialogue and other peaceful means," Lavrov said.

Lavrov's remarks were made at a press conference after he met with visiting Burundian External Relations and International Cooperation Minister Laurent Kavakure.

On Tuesday's deadly shelling of passenger bus in eastern Ukraine, Lavrov insisted that a thorough and objective investigation should be conducted before making unwarranted charges.

"We expect the OSCE mission that is now at the scene to honestly conduct all necessary investigative measures," Lavrov said.

"We seek for justice and truth. We hope everyone else would do the same instead of using the tragedy to justify actions that would only lead to more severe confrontation and to military scenario."

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.