"There is a threat of a point of no return, a moment when the escalation can no longer be stopped and we will literally stand on the threshold of war in Eastern Europe," Steinmeier said in a letter published by the Frankfurter Allgemeine Zeitung on Tuesday.
The Foreign Minister also put forward a plan for deescalating the crisis, including a new international conference to replace the failed Geneva agreements. He also called upon all parties to commit to not disrupt Presidential elections in Ukraine later this month and to work for the disarmament of militant groups.
Ruling out military intervention as "not an option," Steinmeier insisted on the importance of achieving a consensus around these points.
"There is only a chance for success when the most important parties, above all Moscow and Kiev, are ready to go down such a path together," he wrote.
The Foreign Office on Monday raised its travel warning for Ukraine and said on its website it “strongly” advised against travel to the south and east of the country.
A travel warning was already in place for Crimea which has been annexed by pro-Russian separatists.
But violence has spread to other areas of Ukraine with 42 people killed in the southern city of Odessa on Friday and dozens more in fighting around the separatist city of Sloviansk in recent days.
“In light of the latest developments we must assume that representatives of the media are in particular danger of being held or arrested by separatists," the Foreign Office said in a statement.
On Saturday four German hostages who had been held in the eastern Ukraine town of Slavyansk for a week were released.
Four Ukrainian troops were killed and 30 injured in fighting around the town on Monday. The Kiev government also confirmed the deaths of 30 pro-Russian separatists.