Ukraine on Tuesday pressed NATO to come up with a "comprehensive answer" to Russian aggression in the Black Sea, as the alliance treads carefully for fear of escalating tensions further.
Ukrainian Foreign Minister Pavlo Klimkin hinted that at least one NATO member was ready to enhance its presence in the Black Sea in response to a call from Kiev following Russia's seizing of ships and sailors in the Kerch Strait.
NATO foreign ministers meeting in Brussels discussed the Azov Sea standoff but did not agree any concrete new measures to help Ukraine.
"What is critically important is to have a very clear and comprehensive answer to Russian acts of aggression... (and) Russian abuses of Black Sea security," Klimkin told reporters.
The clash last week off the coast of Crimea, annexed by Moscow in 2014, left 24 Ukrainian sailors and three navy ships in Russian hands and sent tensions soaring.
European leaders have rebuffed Ukrainian calls for more support against Moscow, but Klimkin indicated that a NATO country was ready to step up, without giving clear details.
"This presence will be enhanced and we have to see which country will be the pioneer. You will hear that not from us but from the alliance member," he said.
NATO Secretary General Jens Stoltenberg repeated a call for Russia to return the sailors and ships and ensure freedom of navigation in the Azov Sea, an offshoot of the Black Sea home to key Ukrainian ports.
He said the alliance had stepped up its presence in the area over the past year, but announced no new practical help for Ukraine.
The United States is pressing Europe to "show some leadership" on the Azov Sea crisis.
"We really want to see European allies do more," a senior US State department official said.
"We want to see European allies take greater responsibility for a security problem that's just 200 miles from Germany's border."
But European countries -- some of which have strong business links to Russia -- are deeply wary of doing anything that might exacerbate the situation.
"We will continue to make every effort to ensure that this conflict does not turn into a serious crisis, and that can only be achieved with a political solution," German Foreign Minister Heiko Maas said.
Klimkin said he would use talks with EU officials next week to ask whether the international response could include barring Russian commercial shipping from international ports.
Ukraine has accused Moscow of blocking merchant vessels from entering and leaving Azov Sea ports.
But Kiev said Tuesday that Russia had begun allowing some ships to enter Ukrainian ports on the Sea of Azov, in what could signal an easing of tensions in the flashpoint area.