Ukraine has accused Russia of removing weapons and equipment - including toilets - from navy boats it returned after seizing them in the Black Sea.
"[Russia] removed even dome lights, sockets, and toilet bowls," Ukraine's navy commander Ihor Voronchenko said.
But Russia's Federal Security Service (FSB) said the ships were returned in "normal condition and with good plumbing".
The boats, which were seized last November, were handed over on Monday.
The 24 Ukrainian sailors on board the ships were returned in September in a prisoner swap deal.
Video footage reportedly from inside one of the vessels appears to show a toilet in place and intact, but it is unclear when it was shot.
Ukraine's President Volodymyr Zelensky inspected the two gunboats, Berdyansk and Nikopol, and the Yana Kapa tug on Thursday at the Ukrainian port of Ochakiv, near the coastal city of Odesa.
According to Russian state news agency Tass, Mr Zelensky later told reporters that equipment was "partially missing".
"The admiral and I had a conversation, and some things cannot be disclosed, but part of the weaponry is missing," he said. "I noticed the condition and there will be an investigation. We will definitely contact the Russian side so that it returns everything that was there."
The FSB, however, said on Thursday that no complaints were made at the time of the handover, and that documents had been signed accepting the condition of the ships.
"If during the transition... the Ukrainian side managed to bring the plumbing to an inadequate state, then this is the problem of the Ukrainian side," it said.
A short video was later tweeted by Russian reporter Alexander Kots, who wrote: "Ahaha! And the toilet is in place."
Ахаха! А унитаз-то на месте pic.twitter.com/4dLkZ0cBqD— Александр Коц (@sashakots) November 21, 2019
Russian forces annexed Ukraine's Crimea peninsula, which has a Russian-speaking majority, in March 2014, drawing international condemnation. The seizure of the vessels a year ago as they attempted to pass through the Kerch Strait between Crimea and Russia led to a serious escalation in tensions.
When Russia agreed to return the ships, it was seen as marking an improvement in the relationship between the two countries.
How and why were the boats seized?
On the morning of 25 November 2018, the three vessels tried to sail from the Black Sea port of Odessa to Mariupol in the Sea of Azov.
Ukraine said that as they sailed towards the Kerch Strait, they were intercepted by Russians ships, which rammed the tug. The vessels continued for a short distance, but were then prevented from travelling further by a tanker.
Russian forces opened fire and several Ukrainian sailors were injured.
Ukraine called it an act of Russian aggression, saying the Black Sea was free for shipping and that annexed Crimea belonged to Ukraine.
A 2003 Russia-Ukraine treaty stipulates unimpeded access to the Kerch Strait and Sea of Azov. Moscow, however, said the ships had illegally entered its waters.
The boats were held in Kerch, and all 24 sailors on board were detained.
What's the background to this?
The shallow Sea of Azov lies east of Crimea, and south of the Ukrainian regions partially seized by pro-Russian separatists.
The two Ukrainian ports on its northern shore - Berdyansk and Mariupol - are used to export grain and products such as steel and coal.
The 2003 treaty between Ukraine and Russia guaranteed free navigation for both countries' vessels.
But in recent years Russia has been inspecting ships going to or from Ukrainian ports.
More than 13,000 people have been killed in the eastern Donetsk and Luhansk regions since separatists moved against the Ukrainian state in April 2014.
Ukraine and the West accuse Russia of sending its troops to the region and arming the separatists. Moscow denies this but says that Russian volunteers are helping the rebels.