Oren Dorell

USA TODAY

On the same day that NATO warned of Russia moving combat troops into eastern Ukraine, Russia announced Wednesday that it will restart long-range bomber flights near the U.S. from the Caribbean to the Gulf of Mexico.

The muscle-flexing announcement by Russian Defense Minister Sergei Shoigu came just after Russian President Vladimir Putin met with world leaders in China for the Asia Pacific Economic Cooperation summit.

The strategic bombers, capable of carrying nuclear weapons, will also conduct flights along Russian borders and over the Arctic Ocean, Shoigu said.

"In the current situation, we have to maintain military presence in the western Atlantic and eastern Pacific, as well as the Caribbean and the Gulf of Mexico," he said. The flights will conduct "reconnaissance missions to monitor foreign powers' military activities and maritime communications," he said.

A senior U.S. military official told the Associated Press that Russia never flew bomber patrols over the Gulf of Mexico, even during the Cold War.

The announcement came amid a spike in reports of Russian military violating NATO country borders and airspace, and a few hours after NATO's supreme allied commander, U.S. Gen. Phillip Breedlove, warned that Russia had sent artillery and men into eastern Ukraine.

"We have seen columns of Russian equipment, primarily Russian tanks, Russian artillery, Russian air defense systems and Russian combat troops entering into Ukraine," Breedlove said.

Similar statements were issued in recent days by the Organization for Security and Cooperation in Europe (OSCE), the White House and Ukrainian authorities, who say pro-Russian separatists appear on the verge of a new offensive that threatens communities between the Russian border and Ukraine's Crimea region, which Russia annexed in March.

Maj. Gen. Igor Konashenkov, spokesman for the Russian Defense Ministry, denied the assertions of sending troops into Ukraine as "unfounded statements."

Ukrainian President Petro Poroshenko warned this week that the town of Berdyansk is in particular danger.

The White House warned that Russian aggression would violate a cease-fire agreement signed Sept. 5 in Minsk, Belarus, by the separatist leaders, Putin and Poroshenko.

If Russia continues "escalating the situation," it will experience continued economic disruption from U.S. and international sanctions, said Ben Rhodes, who is President Obama's deputy national security adviser.

In August, as Russian tanks and troops were rolling across Ukraine, Putin gave a warning of his own.

"I want to remind you that Russia is one of the most powerful nuclear nations," he said while visiting a youth camp near Moscow. "This is a reality, not just words." Russia, he said, is "strengthening our nuclear deterrence forces."

Contributing: Tatyana Goryachova in Berdyansk, Ukraine; the Associated Press