Alliance chief Jens Stoltenberg praised Ukraine for its "calm and restraint" during the recent naval standoff with Russia in the Azov Sea and said NATO support for Kiev would continue.

After talks with Ukrainian President Petro Poroshenko, Stoltenberg repeated a call for Russia to free sailors seized in the Azov Sea clash last month.

"Today, I told President Poroshenko that we will deliver secure communications equipment for the Ukrainian Armed Forces by the end of this year," Stoltenberg said.

"We are also supporting Ukraine to improve its naval capabilities, logistics and cyber defence."

Earlier this week the EU said Russia had prepared the ground for the sea clash with a year-long campaign of disinformation about Kiev and NATO's plan for the Azov Sea.

Stoltenberg took aim at Russia's "destabilising behaviour", particularly in Ukraine where a conflict rages in the east between the government and separatists supported by Moscow.

"We see that in eastern Ukraine where ceasefire violations are reported daily, including with weapons banned under the Minsk Agreements," Stoltenberg said.

The Minsk agreements were struck to end the conflict, which began following the annexation of Crimea by Russia, but they have not been successful.

Stoltenberg also said that the Organization for Security and Co-operation in Europe (OSCE) monitoring mission in Ukraine was facing restrictions.

"They are regularly prevented from moving freely and their observation drones are jammed and shot down," Stoltenberg said.