SEVASTOPOL, Ukraine (AP) — Russian President Vladimir Putin ordered tens of thousands of Russian troops participating in military exercises near Ukraine's border to return to their bases as U.S. Secretary of State John Kerry was on his way to Kiev. Tensions remained high in the strategic Ukrainian peninsula of Crimea with troops loyal to Moscow firing warning shots to ward off protesting Ukrainian soldiers.
The massive military exercise in western Russia involving 150,000 troops, hundreds of tanks and dozens of aircraft was supposed to wrap up anyway, so it was not clear if Putin's move was an attempt to heed the West's call to de-escalate the crisis that has put Ukraine's future on the line.
It came as Kerry was on his way to Kiev to meet with the new Ukrainian leadership that deposed a pro-Russian president, and has accused Moscow of a military invasion in Crimea. The Kremlin, which does not recognize the new Ukrainian leadership, insists it made the move in order to protect Russian installations and its citizens living there.
On Tuesday, Russian troops who had taken control of the Belbek air base in the Crimea region fired warning shots into the air as around 300 Ukrainian soldiers, who previously manned the airfield, demanded their jobs back.
About a dozen Russian soldiers at the base warned the Ukrainians, who were marching unarmed, not to approach. They fired several warning shots into the air and said they would shoot the Ukrainians if they continued to march toward them.
The shots reflected tensions running high in the Black Sea peninsula since Russian troops — estimated by Ukrainian authorities to be 16,000 strong —tightened their grip over the weekend on the Crimean peninsula, where Moscow's Black Sea Fleet is based.
Ukraine has accused Russia of violating a bilateral agreement on conditions of a Russian lease of a naval base in Crimea that restricts troop movements, but Russia has argued that it was acting within the limits set by the deal.
Russia's ambassador to the United Nations, Vitaly Churkin, said Monday at the U.N. Security Council that Russia was entitled to deploy up to 25,000 troops in Crimea under the agreement. Churkin didn't specify how many Russian troops are now stationed in Crimea, but said that "they are acting in a way they consider necessary to protect their facilities and prevent extremist actions."
Churkin said that Russia wasn't trying to ensure the return to power of fugitive President Viktor Yanukovych, but still considers him the legitimate leader of Ukraine and demands the implementation of a Western-sponsored peace deal he signed with the opposition that set presidential elections for December. Russian envoy at those talks did not sign the deal. Yanukovych fled the capital hours after the deal was signed and ended up in Russia, and the Ukrainian parliament set the presidential vote for May 25.
There was no sign of tensions elsewhere in Crimea early on Tuesday. A supposed Russian ultimatum for two Ukrainian warships to surrender or be seized passed without action from either side, as the two ships remained anchored in the Crimean port of Sevastopol. Russian Defense Ministry spokesman Vladimir Anikin said late Monday that no ultimatum had been issued.
Early on Tuesday, the Kremlin said Putin ordered troops participating in military exercises alongside Russia's western border to return to their permanent bases. The order was in line with an earlier plan to complete the exercise early this week.
The maneuvers, which Putin ordered on Wednesday involved scrambling fighter jets to patrol Russia's western frontiers and stoked fears that the Kremlin might send troops into Russian-speaking regions in eastern Ukraine.
In Brussels, meanwhile, the ambassadors of NATO's 28 member nations will hold a second emergency meeting on Ukraine on Tuesday after Poland, which borders both Russia and Ukraine, invoked an article calling for consultations when a nation sees its "territorial integrity, political independence or security threatened," the alliance said in a statement.
President Barack Obama has said that Russia is "on the wrong side of history" in Ukraine and its actions violate international law. Obama said the U.S. was considering economic and diplomatic options that will isolate Russia, and called on Congress to work on an aid package for Ukraine.
In return, Russia's agricultural oversight agency issued a statement Tuesday declaring the reversal of its earlier decision to lift the ban on imports of U.S. pork. It said the existing U.S. system of checks don't guarantee its safety.
Putin's economic advisor, Sergei Glazyev, said that Russia can develop financial ties with other nations to offset any potential Western sanctions.
The European Union's foreign ministers on Monday threatened Moscow with halting talks on visa liberalization and negotiations on further economic cooperation unless Russian troops on the Crimean peninsula pull back over the next three days.
The bloc's 28 heads of state and government will hold an emergency meeting on the situation in Ukraine on Thursday that will decide on imposing the sanctions if there is no de-escalation on the ground, EU foreign policy chief Catherine Ashton said.
Ivan Sekretarev in Sevastopol and Vladimir Isachenkov in Moscow contributed to this report.