The United States special envoy for Ukraine said Saturday that Washington would consider providing more armaments to the country's army.

Envoy Kurt Volker told reporters in Kyiv that Ukraine has improved its defense capabilities in recent years, but "there are still some gaps in those capabilities. And wherever those gaps are, we are prepared to sit down and talk with Ukraine about what their needs are. They can buy things through our foreign military sales," The Associated Press said.

U.S. President Donald Trump this year reversed the Obama administration's refusal to provide lethal aid to Ukraine and has sent more than 200 Javelin anti-tank rockets.

Volker said the United States is concerned about the expansion of Russian naval operations in the Sea of Azov, which borders Ukraine, Russia and the Russia-annexed Crimean Peninsula.

Read alsoVolker: World must keep situation in Donbas under public spotlight

"We do not accept Russian claims about territory in the waters. We believe the presence of Russian military forces has become a provocative, aggressive step, so we are very concerned about that," he said.

The Russian-led forces in eastern Ukraine have long threatened the Azov port of Mariupol; taking the city would be a key step toward their establishing a land corridor between Crimea and Russia.

The U.S. envoy also criticized the elections that de-facto leaders in Russian-occupied Donbas have called for November in two eastern regions, saying any voting would be a "completely illegitimate exercise."

He criticized Russia's resistance to full deployment of a United Nations peacekeeping mission in eastern Ukraine, where more than 10,000 people have been killed since 2014.

"Russia is insisting this be negotiated directly with the proxy entities," Volker said, referring to the self-declared "republics' governments" in Donetsk and Luhansk regions.

"Russia is, in fact, the decision-maker" in eastern Ukraine, he added.