Russia staged massive military exercises near Ukraine’s border on Thursday in what authorities there feared could be a precursor to another attack.

Andriy Parubiy, the head of Ukraine’s National Security and Defense Council, which advises the country’s president, claimed Russia had deployed more than 80,000 soldiers near the border, along with 270 tanks and 140 combat aircraft. “Ukraine today is facing the threat of a full-scale invasion from various directions,” he said.

Russia insisted that the troop movements were an exercise but until Thursday had denied they were even taking place. If also failed to notify its neighbors of the drills beforehand.

The anxiety came as Russia showed no sign of abandoning its occupation of Ukraine’s Crimea, a peninsula that was part of the Russian Empire for almost two centuries before Soviet leaders transferred it to Ukraine, then a Soviet republic, in 1954.

While Russian president Vladimir Putin has denied that his troops invaded the Crimea, he vowed last week to protect Russian speakers and Russian interests in the region.

Earlier, Russia’s Senate gave Putin the authority to invade Ukraine which is home to a 17 percent ethnic Russian minority, according to the latest census. The authorization followed the removal of the country’s elected president, Viktor Yanukovich, after months of protests against his decision to pull out of an associated agreement with the European Union in favor of deeper ties with Russia.

Western leaders have criticized Russia’s aggression and threatened sanctions but otherwise shied away from escalating what is the worst crisis in East-West relations since the end of the Cold War in 1991.

In an unusually robust speech on Thursday, Germany’s chancellor Angela Merkel, whose country has close commercial relations with Russia, warned of “catastrophe” if Putin persisted in his attempt to draw the Crimea into his sphere of influence. “We would not only see it, also as neighbors of Russia, as a threat. And it would not only change the European Union’s relationship with Russia,” she told parliament. “No, this would also cause massive damage to Russia, economically and politically.”

Germany is Russia’s largest buyer of natural gas while total trade between the two countries exceeded €50 billion in 2012.

After emergency consultations in Brussels, NATO this week deployed reconnaissance planes in Poland and Romania to monitor the situation in Ukraine while the United States sent fighter jets to Poland and a warship to the Black Sea in what was described as a routine deployment.

Speaking at the Atlantic Council, a Washington DC think tank, after meeting with American president Barack Obama, Ukraine’s prime minister Arseniy Yatseniuk warned that a restoration of the Soviet Union would be “the biggest disaster of this century.”

The Crimean regional parliament has formally requested annexation by Russia. A referendum to decide the region’s status, which Ukraine’s national government and Western allies say would be illegitimate, is expected to be held on Sunday.