"My husband came with us as far as the border, before returning to Kyiv to fight," said the 36-year-old marketing employee, who did not give her surname.

The young Ukrainian was one of hundreds arriving at the border crossing in the town of Isaccea on the Romanian side of the river on Saturday.

Romania, a former member of the communist bloc now part of NATO and the European Union, fears it could find itself on the frontline against Russia if Moscow overruns neighbouring Ukraine.

Since the beginning of Russia's invasion on Thursday, Romanian border guards have counted more than 25,000 Ukranians crossing into the country.

In the small riverside port of Isaccea, Olga said she intended to spend a few days in Romania, before making her way on to next-door Bulgaria.

Not far off, 40-year-old lawyer Andrey said he feared he had been forced to flee his country for good.

"We will never be able to return to Ukraine," he said bitterly, after crossing the river with his wife and three children.

He said his family had already been forced to flee their home in Ukraine's eastern Donbas region due to the conflict there in 2014, finding refuge in the Ukrainian port city of Odesa.

But now they had been uprooted all over again.

- Russians offshore -

Romania, which shares some 650 km (400 miles) of border with Ukraine, feels for the moment that its NATO membership will protect it from any more serious military consequences.

"Given the regional security dynamic, there is a minimal possibility of the country becoming the target of a conventional offensive action by Russia," the Chief of Defence Staff General Daniel Petrescu said on Saturday.

But, over the past months of growing tensions in the region, Romania has repeatedly demanded reinforcements be sent to NATO's eastern flank.

Its allies have responded.

The United States has sent a squadron of Stryker armoured vehicles and some 1,000 troops in recent weeks to a Romanian base near the Black Sea, adding to the 900 personnel already stationed in the country.

And over the past month, six Eurofighter Typhoon aircraft from German's airforce have joined four similar planes Italy dispatched before the crisis.

France's army chief of staff said on Friday that 500 soldiers would be dispatched to the eastern European country.

The situation has been complicated by Russia's seizure from Ukraine on Thursday of Snake Island, an uninhabited but strategic rocky outcrop in the Black Sea just 45 km (27 miles) from Romania's coastline.

Bucharest and Kyiv both claimed the island, before the International Court of Justice awarded it to Ukraine in 2009.

"We will have to get used to living with the Russians on our border," Defence Minister Vasile Dancu said on Friday, following the island's capture.

"But these are NATO borders. Romania will not be alone in handling this, it will have support if necessary."

- Silver lining -

Romania is however concerned that hydrocarbon companies it has contracted to look for natural gas deposits off its shores might be put off by Russian troops so close to Romanian territorial waters.

Exploration has not yet started, but any findings would be a huge source of gas for the country.

NATO Secretary General Jens Stoltenberg on Friday stressed the Kremlin's objectives were not limited to Ukraine, as it has demanded the military alliance remove all forces and infrastructure from countries that have joined since 1997.

Among those, Russia wants to see an end to the presence of a NATO anti-missile system at the Deveselu military base in southern Romania.

NATO insists the system serves a purely defensive purpose, but Moscow says it considers it a threat.

Beyond the current tensions, sociologist Remus Ioan Stefureac says there is, however, at least one silver lining to the crisis for Romania.

"Since the aggression against Ukraine, Romanians' trust in the EU and NATO has soared to more than 80 percent," he said.

Many Romanians had lost faith in both institutions in recent years, not least because of disinformation originating in Russia.

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STRYKER