Russian President Vladimir Putin said Tuesday that any decision by the United States to supply defensive weapons to Ukraine would fuel the conflict in eastern Ukraine and possibly prompt pro-Russian separatists to expand their campaign there.

Putin, answering a question after a BRICS summit in China about the possibility of the United States supplying Ukraine with heavy weapons, said it was for Washington to decide whom it sold or gave weapons to, but he warned against the move.

Ukraine and Russia are at loggerheads over a war in eastern Ukraine between pro-Russian separatists and Ukrainian government forces that has killed more than 10,000 people in three years. Kiev accuses Moscow of sending troops and heavy weapons to the region, which Russia denies.

The move came amid the ongoing diplomatic row between Washington and Moscow after the U.S. order for Russia to vacate some of its diplomatic properties. This was the latest in a series of tit-for-tat actions that began when former U.S. president Barack Obama, late last year, expelled 35 Russian diplomats.

Russia reserves the right to cut further the number of U.S. diplomatic staff in Moscow, President Putin said, in response to what he called Washington's "boorish" treatment of Russia's diplomatic mission on U.S. soil.

U.S. President Donald Trump took office in January, saying he wanted to improve ties with Russia. Putin also spoke favorably of Trump. But relations have been damaged by accusations from U.S. intelligence officials that Russia sought to meddle in the presidential election. Russia has denied interfering in the vote.

Asked by a reporter if he was disappointed with Trump, Putin said: "Whether I am disappointed or not, your question sounds very naive - he is not my bride and, likewise, I am neither his bride nor bridegroom."

"We are both statesmen. Every nation has interests of its own. In his activities, Trump is guided by the national interests of his country, and I by the interests of mine."

"I greatly hope that we will be able, just as the current U.S. president said, to find some compromises while resolving bilateral and international problems ... taking into account our joint responsibility for international security."