President Medvedev accused Ukraine of trying to rewrite history
Russian President Dmitry Medvedev has made a scathing attack on Ukraine's president, accusing him of "anti-Russian" behaviour.
In a videoblog message on the Kremlin website, Mr Medvedev said he would delay sending a new ambassador to Kiev until relations improved.
Ukraine's President Viktor Yushchenko has forged close links with the EU, US and Nato since coming to power in 2004.
He is expected to run for re-election in Ukraine in January.
In the videoblog, Mr Medvedev commented on a letter he had sent to Mr Yushchenko recently, which he said was "no routine matter".
He accused Mr Yushchenko of having supplied Ukrainian weapons to the Georgian forces who "killed civilians and Russian peacekeepers in Tskhinvali" during the South Ossetia conflict a year ago.
He also accused Mr Yushchenko of bypassing Russia in Ukrainian energy deals with the EU "concerning deliveries of our Russian gas".
Mr Medvedev said the Ukrainian authorities had created problems for the Black Sea Fleet, based in the Crimean port of Sevastopol, in southern Ukraine.
He also accused the Yushchenko administration of driving the Russian language out of Ukrainian media, education and culture, and of trying to rewrite history.
Mr Medvedev said he hoped the situation would return to normal under a new Ukrainian leadership. The BBC's correspondent in Kiev says this was a thinly-veiled reference to Ukraine's presidential election, set for 17 January.
Mr Yushchenko spearheaded Ukraine's pro-Western "Orange Revolution" in 2004, which overturned the election of Viktor Yanukovych, who was backed by Moscow. Election observers had declared the Yanukovych victory to be fraudulent.
Mr Yanukovych now heads the opposition Party of Regions, and opinion polls suggest he could be a strong candidate in the presidential election. His support base is in mainly Russian-speaking eastern Ukraine.
The BBC's Gabriel Gatehouse in Kiev says some Ukrainians will interpret Mr Medvedev's verbal assault as the opening shot in a new Russian campaign to regain the influence that Moscow lost five years ago.
Diplomatic relations had already soured before Mr Medvedev's attack on Mr Yushchenko.
Moscow's previous ambassador to Kiev was recalled in June.
On Monday a councillor at the Ukrainian embassy in Moscow, Ihor Berezkin, left Russia in line with a demand from the Russian authorities.
Last month Ukraine expelled a Russian diplomat.