U.S. forces in Iraq and Syria have not received orders to join Russia in a joint military operation to fight the Islamic State group, also known as ISIS, said spokesman Col. David Warren in a Pentagon press briefing Wednesday. But he said that U.S. troops there were "ready for any operation assigned to them."  Both the U.S. and Russia have said they are stepping up their campaigns in Syria to fight the Sunni militant group in support of France after the attacks in Paris last Friday that killed 129 people.

The U.S. has been working with France to fight ISIS since the U.S. coalition to fight the militant group formed in 2014, but now Russia, which is fighting U.S. allies in Syria, is as well. The new partnership between Russia and France could force the U.S. to cooperate in a joint military operation with a country that has deliberately targeted moderate opposition rebels armed with American weapons in Syria.

Warren's comments Wednesday came just after Russia's military general staff Col. Gen. Andrei Kartapolov said the country was developing plans for joint military operations in Syria with France.  President Vladimir Putin ordered the Russian missile cruiser Moskva, which is deployed in the Mediterranean Sea, to cooperate with the French aircraft carrier Charles de Gaulle.

The French navy's ship sailed from the Toulon naval base south of France and headed for the eastern Mediterranean to support the U.S. coalition. The ship, which has 26 fighter jets on board, will arrive on station in the next few days, France Info radio reported. 

"When the Charles de Gaulle comes to the shores of Syria, joint military work will be organized," Kartapolov said, according to the Associated Press. Kartapolov also said that Russian warplanes on Wednesday attacked oil extraction, transport and refinement facilities in areas controlled by ISIS. French President François Hollande is set to meet Putin in Moscow next week.

The Kremlin confirmed that its cruise missiles targeted Raqqa, the ISIS headquarters in Syria, the Independent reported. Russian officials gave their U.S. counterparts notice ahead of the strikes, the Washington Post reported. Warren said in the briefing Wednesday the U.S. airstrikes over the last several days have targeted ISIS warehouses and convoys in Iraq and Syria.