Syria war planes struck two separate Islamic State of Iraq and Syria (ISIS) convoys near the town of Al Qaim just inside Iraq over the weekend, two well-placed senior U.S. defense officials told Fox News.

The Syrian planes struck on Saturday with the help of Iranian intelligence, sources familiar with the incident said.

There is no bomb damage from the attack, but it is the first time there have been reports of Syrian warplanes having crossed into Iraq since the ISIS fighters swept across the country a week ago.

A U.S. Central Command spokesman would not comment on the reports.

The reports come after a weekend in which violence inside Iraq has intensified in the most serious crisis since the United States withdrew its military forces from the nation three years ago.

Over the weekend, militants posted photos that appeared to show their gunmen massacring scores of captured Iraqi soldiers. The pictures, on a militant website, appear to show masked ISIS fighters loading the captives onto flatbed trucks before forcing them to lie face-down in a shallow ditch with their arms tied behind their backs. The final images show the bodies of the captives soaked in blood after being shot at several locations.

U.S. State Department spokeswoman Jen Psaki said Sunday that a militants' claim of killing Iraqi troops "is horrifying and a true depiction of the bloodlust that those terrorists represent." She added that an ISIS claim that 1,700 were killed could not be confirmed by the U.S.

The U.S. is positioning Naval vessels in the Persian Gulf to assist in the event of an evacuation. Americans already are being moved out of the U.S. Embassy in Baghdad -- according to a senior U.S. official, about 1,000 U.S. Embassy personnel are slated to be moved to other U.S. consulates in Iraq, as well as to Jordan. That represents one-fifth of the 5,000 personnel at the compound, the largest American embassy in the world. The embassy remains open.

Fox News' Jennifer Griffin and The Associated Press contributed to this report.