Russia has warned Ukraine against following through on threats to expel Moscow's ambassador to Kyiv, in the latest sign of tension between the two governments.

The warning from the Russian Foreign Ministry came after Ukraine's pro-Western leaders threatened to send home ambassador Viktor Chernomyrdin, a former Russian prime minister.

It was not immediately clear what Chernomyrdin had done to anger Kyiv.  But Russian news reports have linked the dispute to an interview Chernomyrdin gave last week to Russian newspaper Komsomolskaya Pravda.

In the interview, Chernomyrdin said it is "impossible to come to agreement on anything with the Ukrainian leadership."  He also said the situation could change with different leaders.

Over the past two years, Ukraine has banned several Russian politicians from the country, due to comments they made about Ukraine's Russian-speaking Crimean region.

Bilateral ties further soured when Western-leaning Ukrainian leaders swept to power in 2004, advocating NATO membership and closer economic ties with the European Union.

The two governments also faced off early this year and in 2006 in bitter disputes over Russian natural gas supplies.  

Some information for this report was provided by AP and Reuters.