"It is more than 150,000 Russian troops massing on the Ukrainian borders and in Crimea. The risk of further escalation is evident," Borrell said, declining to give a source for the figure.
He said no new economic sanctions or expulsions of Russian diplomats were planned for the time being, despite saying that the military build-up on Ukraine's borders was the largest ever.
In Washington, the Pentagon said the Russian military build-up was larger than that in 2014 and it was not clear that it was for training purposes.
A U.S. official, speaking on the condition of anonymity, said the Russian build-up numbered in the tens of thousands but was not aware of intelligence that pointed to more than 150,000 Russian troops.
Ukrainian Foreign Minister Dmytro Kuleba, after addressing EU foreign ministers, called on the EU to impose new sanctions on Russia.
Tensions between Moscow and Kyiv have been rising amid the military build-up and clashes in eastern Ukraine between the army and pro-Russian separatists. (Reporting by Robin Emmott and Sabine Siebold. Additional reporting by Idrees Ali in Washington Editing by Alistair Bell)