Ukrainian President Petro Poroshenko has said that Russia is building up forces and weapons in the Black and Azov Seas and does not exclude that the Kremlin might prepare for an attack on Mariupol (Donetsk region) and for blocking Ukrainian exports.

"We see a significant increase in the escalation of tension. Russia has illegally occupied territories and dramatically increased its military groups. For the first time, it deployed a strike aviation group, modern missile systems, modern anti-aircraft systems. We see that the Black Sea Fleet illegally stationed in the annexed Ukrainian Sevastopol was strengthened with submarines, new warships, armed with long-range sea-launched missiles," Poroshenko said in Odesa on Monday at a ceremony to present certificates for new diving equipment to representatives of the Ukrainian Navy.

According to him, Russian naval forces in the Azov Sea have been significantly strengthened.

He noted that Russia had begun to illegally stop and inspect ships heading to Ukrainian ports in the Azov Sea under flags of Ukraine and other states.

"We see that this is being done to block the ports of Ukraine in the Azov Sea, to escalate tension and, possibly, to carry out a military operation - attacks on Mariupol, where exports of products and ferrous metallurgy of Ukraine are conducted, as well as attacks on other ports of the Azov Sea," he said.

Poroshenko said that at the moment the combat readiness of the Ukrainian Navy, as well as their interoperability with allies from NATO member countries and with the security allies in the Black Sea region, is very important.

"We must exert maximum efforts to restore the operational capability of our naval defense component as soon as possible, and be clearly always ready for common defense actions in the Black Sea," the president said.