Former Soviet Union leader Mikhail Gorbachev warned Saturday that tensions between the major powers have put the world "on the brink of a new Cold War."

The 83-year-old accused the West, particularly the United States, of giving in to "triumphalism" after the collapse of the communist bloc a quarter century ago. The result, he said, could be seen in the ability of global powers to prevent or resolve conflicts in Yugoslavia, the Middle East and most recently Ukraine.

Speaking at an event marking the 25th anniversary of the fall of the Berlin Wall, Gorbachev called for new trust to be built through dialogue with Moscow, and suggested the West should lift sanctions imposed against senior Russian officials over its actions in eastern Ukraine.

Gorbachev's comments come at a time of heightened tensions between Russia and the United States, notably over events in eastern Ukraine.

Kiev and its Western allies have accused Russia of arming and fueling a separatist rebellion in breakaway regions of the Ukraine. Fighting between pro-Russian rebels and government forces has so far seen the deaths of 4,000 people.

And despite a current truce being in place, consistent violations by both sides appear to be in evidence. Kiev has also warned of a recent surge of military support by Moscow for the rebel groups.

On Saturday, Associated Press reporters saw more than 80 unmarked military vehicles on the move in rebel-controlled areas of eastern Ukraine, indicating that intensified hostilities may lie ahead.

Three separate columns were seen — one near the main separatist stronghold of Donetsk and two outside the town of Snizhne, 50 miles further east. The vehicles were mainly transportation trucks, some of them carrying small- and large-caliber artillery systems, and at least one armored personnel carrier. Several of the trucks were seen to be carrying troops.

Ukrainian officials said this week that they believe rebel forces have received substantial consignments of weaponry and manpower from Russia. Moscow denies such claims.

It was not immediately possible to establish the provenance of the vehicles seen Saturday. Separatists have always insisted they are armed with equipment captured from Ukrainian forces, but the sheer scale and quality of their armaments have strained the credibility of that claim.

Ukrainian National Security and Defense Council spokesman Volodymyr Polevoy said rebel reinforcements have also been observed moving toward front-line locations around 95 miles northeast of Donetsk, in the Luhansk region.

Polevoy said rebel authorities are boosting their ranks by forcibly mobilizing residents in a number of occupied towns.

Despite a cease-fire being reached in September, Ukrainian and rebel troops engage on a regular basis, with some of the heaviest fighting focused on Donetsk airport.

One government paratrooper was killed Friday by a sniper at the airport, military authorities said in a statement. Polevoy said two other Ukrainian troops were killed on the same day, but gave no details.

In Beijing, U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov met Saturday on the sidelines of the Asia-Pacific Economic Cooperation conference for what was expected to be a discussion about the unrest in eastern Ukraine.

Asked if Russia still respects the legitimacy of the cease-fire agreement, Lavrov said it is for the "rebels and the government" of Ukraine to finalize a disengagement line — a process that he said is continuing.

Tensions between Ukraine and Russia rose further after the rebels held an election last Sunday that Ukraine and the West denounced as a violation of the truce. Russia, however, quickly lent its support to the vote.

Al Jazeera and wire services