Ukrainian ports will remain closed until Russia's invasion ends, the head of Ukraine's Maritime Administration said on Monday, adding that the port of Mariupol has sustained damage from Russian shelling.

Russia invaded Ukraine on Feb. 24, calling its actions a "special operation".

"The ports will be shut until the end of Russian aggression on our territory and (we) restore the ability to provide maritime security for commercial vessels," Vitaliy Kindrativ told Reuters in emailed comments.

Kindrativ said the authorities were still assessing the extent of damage in Mariupol, a prominent port located on the Sea of Azov, adding that other ports had also seen some damage, which was "not critical".

"But I think that final calculation will be done after the end of Russian aggression as there is still a great threat of landing of Russian troops through ports, which may cause great destruction of port infrastructure," he said.

Many shipping companies have suspended sailings to affected Black Sea ports with insurance premiums for voyages soaring in recent days and at least three commercial ships hit by bombs since Feb. 24.

Prospects for Russian and Ukrainian spring grain, which is supposed to start soon, could also be affected by the conflict.

Navigation in the Azov Sea was stopped on Feb. 24, and while Russian Black Sea terminals continue to load and ship grain, a big question mark looms over new shipments due to a lack of freight offers, consultancy Sovecon said.

Kindrativ added that there were about 100 foreign flagged ships now "blocked in Ukrainian seaports by the Russian navy".

"They will be able to sail after the Russian navy removes its warships from our sovereign water, sea routes will be safe for navigation, and when the ship masters get clearance from Ukrainian seaport captains," he said.

The port of Berdiansk located on the Sea of Azov was also hit by shelling on Monday, but it was unclear what was happening at the port.