According to multiple media reports, the Kremlin has hired between 10,000 and 20,000 mercenaries to fight in eastern Ukraine, including infantry fighters from Syria and Libya.

The official, who spoke to reporters at a briefing in Washington on condition of anonymity, said it is difficult to break down the number of fighters from each country but noted that they were all hired by the private military company.

The official said that Syria and Libya were used as a mass against the Ukrainian resistance.

The official said that they don't have any heavy vehicles or weapons. It is much more infantry.

In smaller numbers, Russia has deployed Syrian fighters in Ukraine. Several hundred Syrian mercenaries arrived in the country on March 31, including soldiers from an army division that worked with Russian officers supporting the Assad regime, according to The New York Times.

Russian Defense Minister Sergei Shoigu said last month that 16,000 volunteers from the Middle East had signed up to fight. According to The Kyiv Independent, Ukrainian intelligence claimed that Russia had struck a deal with Haftar to recruit mercenaries.

According to The Guardian, theWagner Group, which has close ties to Russian President Vladimir Putin, has been assisting Moscow in transporting soldiers to Ukraine.

Ukrainian President Volodymyr Zelenskyy said on Monday that Moscow has launched a renewed offensive on the region.

As the war continues, the European official said that Russian troop morale has been failing, while Ukrainian soldiers have been encouraged by the sinking of the Russian ship.

The Pentagon's John Kirby said on Monday that the US intelligence shows that Russia is preparing for more aggressive operations in eastern Ukraine.