Putin responded by warning NATO threatens Russia to pay a "heavy price" if it attacks Ukraine

NATO threatened Russia that it would pay a "heavy price" if it invaded Ukraine, while Russian President Vladimir Putin warned the West against crossing the Kremlin's "red lines".

NATO warned Russia on Tuesday that it would pay a heavy price if it invaded Ukraine, while Russian President Vladimir Putin warned the West not to cross the Kremlin's "red lines".

On Tuesday, representatives of the countries affiliated with the coalition met in Riga, the capital of Latvia, and discussed ways to deter any Russian invasion of Ukraine, after fears of a Russian attack increased after Moscow mobilized tens of thousands of its soldiers and strengthened its military deployment on the border between the two countries.

"Any Russian invasion of Ukraine will be very costly and will have political and economic consequences for Russia," NATO Secretary General Jens Suttletenberg said after the meeting.

Stoltenberg indicated that member states of the alliance could impose "economic sanctions and take political measures" against Russia, without giving further details.

"We have to be prepared for the worst, and we have to send a message to Russia that it should not make a military incursion into Ukraine," he said. US Secretary of State Anthony Blinken had earlier warned of "grave consequences" for any Russian invasion of Ukraine. Moscow, which annexed Crimea from Ukraine in 2014 and supports separatists in northern Ukraine, has vehemently denied it was planning an attack, blaming NATO for stoking tensions.

On Tuesday, Russian President Vladimir Putin said that military exercises and other moves by the West and Ukraine threaten Russia's security, warning against crossing the Kremlin's "red lines".

"Look, they talked about a possible Russian military intervention in Ukraine at the beginning of the year. But as you can see, that didn't happen," he added.

The new reinforcements follow similar ones in the spring, when Russia massed nearly 100,000 troops on the Ukrainian border and later announced their withdrawal.

NATO diplomats say the bloc is still unsure of Russian President Vladimir Putin's intentions, but ministers will discuss contingency plans in the event of a Russian invasion.

The US-led alliance is trying to show the Kremlin that it will incur a heavy cost if Ukraine is threatened, but it has not provoked Moscow into new aggression.

Officials are discussing the possibility of providing additional support to the Ukrainian army and the possibility of strengthening the bloc's forces deployed on the eastern bank of the alliance.

But they point out that Ukraine, aspiring to join NATO, and whose foreign minister will participate in the two-day meeting, is not covered by the alliance's comprehensive defense treaty.

Kiev called for urgent action to "deter" any Russian invasion of its lands, and indicated that the Russian military operation could begin "in the blink of an eye."

"Hybrid attack"

The meeting comes at a time when the bloc's eastern borders are witnessing turmoil, as allied countries, especially Poland, Lithuania and Latvia, members of the North Atlantic Treaty Organization, seek to address a migrant crisis that the West accuses of fueling Moscow-backed Belarus.

Those countries accuse Belarus of sending thousands of migrants, most of them from the Middle East, to its borders in a "hybrid attack" in retaliation for European Union sanctions against Minsk.

Belarusian President Alexander Lukashenko rejects these accusations.

NATO expressed "solidarity" with its members in the east, but refrained from direct intervention, given that the current threats do not rise to the level of actual aggression.

Poland proposed to reinforce the NATO forces deployed on its eastern borders.

However, it appears that the effort to launch emergency consultations under Article 4 of the treaty founding the alliance has been postponed for the time being.

Border tension eased a bit as some migrants began returning to Iraq, but Warsaw and Vilnius insist that the crisis is still far from over.

The European Union, the United States and other members of the North Atlantic Treaty Organization are scheduled to impose a new set of sanctions on Belarus in the coming days.

"Lukashenko must stop using the weak as pawns in a political game against other countries," Stoltenberg said.

He continued, "We are working closely with the European Union, because neither the European Union nor NATO has sufficient tools. But together, we can provide a strong response to what is happening."