Russia's foreign minister has said that talks with Ukraine have failed to agree a ceasefire but all objections to a Russian humanitarian convoy entering the country have now been dropped.

Sergei Lavrov said on Monday that "all questions" regarding the mission had been removed and agreement had been reached with Ukraine and the International Committee of the Red Cross (ICRC), but it was unclear if he was referring to security guarantees, which the ICRC wants to receive from all sides including pro-Russia rebel fighters, before accompanying more than 200 trucks into Ukraine.

An ICRC spokeswoman in the region where the trucks were parked said earlier it was still waiting for the security guarantees.

The convoy has been parked for days in Russia near the border amid objections from Kiev, which believes the convoy could be a Trojan horse for Russia to get weapons to the rebels – a notion that Moscow has dismissed as absurd.

Lavrov met late on Sunday in Berlin with counterparts from Ukraine, France and Germany; the talks concluded with agreement for the four to meet again.

He said there had been no progress towards a ceasefire in eastern Ukraine, where pro-Russia rebels are facing a sustained advance by government troops.

"One place where we cannot report positive results is in, first and foremost, establishing a ceasefire and (starting) a political process," Lavrov told a Berlin press conference shown live on Russian state television.

He accused Kiev of continually changing demands over what it would take to establish a truce and said he used the Berlin meeting to "reaffirm the Russian position, which is that a ceasefire … must be unconditional".

The four-month-old conflict in Ukraine's Russian-speaking east has reached a critical phase, with Kiev and western governments watching nervously to see if Russia will use troops massed along its border to intervene in support of the increasingly besieged pro-Russia rebels.

Russia has repeatedly said it has no plans to invade and Lavrov again denied Moscow is helping the rebels. He defended the military buildup on Russia's border, saying: "We must be alert … when several kilometres from our border a real war is under way."

Ukrainian government forces pressed pro-Russia separatists in fighting overnight into Monday, encircling the rebel-held town of Horlivka and taking control of smaller settlements in eastern Ukraine, the military said.

A military statement said it suspected the rebels had fired back with a powerful Russian-made Uragan missile system south-east of Donetsk near the village of Novokaterinivka, their first use of the weapon.

It gave no indication of casualties on either side and the rebels made no immediate comment.

Horlivka, a town of more than 230,000 which has been in the hands of the rebels since early on in the conflict, has strategic value because it lies just north of the main road linking Donetsk and Luhansk.

The separatist conflict erupted after Russia annexed Ukraine's Crimean peninsula following the ousting of a Moscow-backed president in the capital, Kiev. Separatists occupied key buildings in towns across the Russian-speaking east, declaring "people's republics" and saying they wanted to join Russia.

Kiev and the west have accused the Kremlin of shelling Ukrainian positions at the border and giving the rebels open access to deliveries of Russian fighters and arms, including missile systems. Moscow denies providing support to pro-Russia rebels.