For the second time in a month, Russian jets bombed US-trained rebels in Syria, this time conducting two separate strikes on Tuesday, multiple US military officials in Baghdad told Fox News.

The rebels had been trained by the Central Intelligence Agency, according to officials.

The first Russian strike Tuesday involved a flight of Russian Backfire bombers from Russia, likely from Mozdok airbase in Ossetia, Russia, the sources said.

Tu-22M backfire bombers first appeared over Syria in November, less than two months after the start of their air campaign to support embattled President Bashar al-Assad. The strike killed an unknown number of rebels.

The second strike killed rebels and Syrian refugees near Syrian's border with Jordan. Again, there was no confirmation on casualties.

Last month, the Russian Air Force bombed Pentagon and CIA backed rebels near al-Tanf, located near the Iraqi and Jordanian border in southern Syria. After the first strike, the US military called the Russians on a special emergency hotline between the two nations. The Russians ignored the request from the US military to stop bombing and launched a second strike.

Fox News asked Gen Joe Votel about the Russian attack this week, "I am obviously concerned about that. It's hard for me to understand what they are hoping to achieve with those strikes.”