Russian forces have struck two vessels carrying weapons and military equipment to Ukrainian ports near Odesa, the Russian Defence Ministry has announced.
Reuters could not independently verify the report.
The ministry on Wednesday said Russian forces had also hit a fuel storage facility in Odesa, two additional vessels in the port of Pivdennyi near Odesa, and another vessel northwest of Zmiinyi (Snake) Island in the Black Sea.
It said, without providing evidence, that all the vessels were being used to transport military supplies to Ukraine.
Russia and Ukraine have both stepped up attacks in recent weeks on shipping in the Black Sea and Sea of Azov, driving wheat prices higher.
Ukraine President Volodymyr Zelenskiy said a massive Russian attack on Ukraine was likely on Wednesday evening, adding that the safety of Ukrainians depended on the willingness of Kyiv's allies to provide anti-missile defences.
"It is important that our partners fully understand what is happening and that the protection of people's lives depends directly on their willingness, or lack of willingness, to provide air defence missiles," Zelenskiy said.
"This primarily concerns the United States and those partners that have missiles for the Patriot air systems and are able to support our defence with them."
Ukraine's Air Force on Wednesday said one of its F-16 fighter aircraft had crashed, but the pilot was safe after ejecting.
The force said the aircraft was carrying out a frontline assignment to intercept Russian airborne targets when a malfunction occurred.
It said the pilot was found safe and transported to a medical institution for treatment. Experts were examining the site where the aircraft came down.
Ukraine has received US-made F-16s from a number of NATO countries, including the Netherlands and Denmark.
Meanwhile, the Russian rouble weakened by 1.9 per cent against the US dollar on Wednesday to cross the level of 80 to the dollar for the first time since April 3, LSEG market data showed.
The rouble has weakened by 14 per cent against the dollar since May 20 as Ukraine intensified attacks on Russian refineries and infrastructure, which resulted in fuel shortages and rising inflation.
Against the Chinese yuan, Russia's most traded foreign currency, the rouble has weakened by 1.0 per cent to trade at 11.8 roubles per yuan.
Analysts said that an end to seasonal tax payments when Russian companies sell foreign currency to pay their taxes in roubles, as well as unstable prices for oil, Russia's main export commodity, contributed to the rouble's weakness.
"In this situation, pressure on the rouble may persist in the near term," said Bogdan Zvarich from PSB bank.
