Medvedev was initially scheduled to celebrate Navy Day on Sunday by visiting the Crimean port of Sevastopol, where the Russian Black Sea Fleet is based, a Russian defence ministry source said.

“The status of the parade in Sevastopol has been downgraded,” the source, who asked not to be identified, told AFP.

Medvedev, who was expected to meet Ukrainian President Viktor Yanukovych in Sevastopol, is now set to visit the port of Baltiisk in the Russian exclave region of Kaliningrad for the festivities, he said.

General Nikolai Makarov, the Russian armed forces’ chief of staff, was expected in Sevastopol, the source added.

He could not give an official reason for the change of plan, adding it spoke of “remaining problems on both sides”.

Medvedev’s spokeswoman Natalya Timakova denied the Kremlin chief had any plans to go to Sevastopol. She told AFP the date of the future high-level regular talks still needed to be agreed upon.

A Ukrainian foreign ministry spokesman issued a similar statement.

But the deputy head of the Sevastopol city administration Sergei Savenkov told the Interfax-Ukraine news agency earlier this month that preparations were underway to host Medvedev and Yanukovych on July 31.

Russia has maintained its historic Black Sea fleet base in Sevastopol since the collapse of the Soviet Union in 1991 and the Russian lease on the facility was set to expire in 2017.

Medvedev and Yanukovych however stunned observers last year when they agreed on a deal for Moscow to maintain its fleet in Ukraine until at least 2042 in exchange for cheaper natural gas.

Yanukovych has worked hard to improve relations between Moscow and Kiev since defeating the leaders of the pro-Western Orange Revolution in presidential elections last year.

But observers say Ukraine has over the past months grown disillusioned with the prospects of closer ties with Moscow and its attempts to strong-arm Kiev into joining the Russian-led customs union.

Moscow fears Ukraine may be ramping up its ties with NATO despite its non-aligned status. Russia last month protested the arrival of a US Navy cruiser equipped with a ballistic missile defence system in the Black Sea to take part in naval exercises with Ukraine.