Moscow (AFP) - Germany's foreign minister said Tuesday he was not optimistic about an end to the conflict in Ukraine because of a "dangerous" escalation of fighting in the east.

Frank-Walter Steinmeier made the downbeat assessment after NATO's secretary-general spoke of a "very serious build-up" of troops, artillery and air defence systems inside Ukraine and on the Russian side of the border.

Steinmeier was the first senior European minister to visit Moscow since July, in a sign of how relations between the West and Russia have dived to a post-Cold War low over the conflict in eastern Ukraine.

"There are no grounds for optimism in the current situation," Steinmeier said at a press conference after talks with his Russian counterpart Sergei Lavrov in Moscow.

The German minister warned of a "dangerous situation developing" in Ukraine, which he visited earlier in the day.

He appealed to all sides to stick to the Minsk ceasefire agreement signed on September 5, which appears increasingly threadbare.

Steinmeier said it would be a "great loss" to abandon the frequently violated ceasefire deal, which has stopped most fighting but failed to prevent frequent flare-ups at strategic locations.

"The Minsk agreements are not perfect but it is the only thing that has been supported by all the key players -- the European Union, the United States, the parties to the Ukrainian conflict and Russia," he said.

Before Tuesday's meeting got under way, Lavrov said his government hoped "that the 'point of no return' has not yet been crossed" in Russia-Europe relations.

-- Russia 'has a choice' --

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NATO warns of 'very serious' Russian military build-up in Ukraine