A week after Russia surprised the U.S. and became overtly involved in the Syrian Civil War, senior U.S. lawmakers have begun looking into whether intelligence agencies overlooked or misjudged warning signs of Moscow's intentions, congressional sources told Reuters.

The House and Senate Intelligence committees are reportedly concerned that spy agencies were slow to grasp the full scope of Russia's plans for Syria, which began on Sept. 30 with airstrikes backing Syrian President Bashar al-Assad's forces.

Intelligence analysts were particularly caught off guard by the speed and aggressiveness of Russia's use of air power, as well as its targeting of U.S.-backed rebel groups fighting to overthrow Assad, according to officials who spoke to Reuters on the condition of anonymity.

"They saw some of this going on but didn't appreciate the magnitude," one of the sources told Reuters, while one source said agencies had lagged for about a week before voicing "full-throated alarm" about Russia's true intention. That could have been because, as another source said, U.S. analysts initially believed Russia's military buildup near the Syrian port of Latakia was simply for a brief military exercise, rather than a sustained use of force designed to prop up Assad.

On Wednesday, four Russian warships in the Caspian Sea launched 26 long-range cruise missiles at 11 Islamic State targets in Syria, with the missiles traveling 980 miles through Iranian and Iraqi airspace, reported the Guardian. Moscow and Syria also conducted coordinated assaults on Wednesday against opposition rebel groups in various towns in western Syria, which saw Russian fighter jets reportedly bombing a series of targets as Assad's forces attacked from the ground. The U.S. ambassador to NATO told Reuters that Moscow also has a battalion of troops on the ground backed by some of its most advanced tanks.

If intelligence agencies did indeed overlook critical details of Russia's intentions, it would mark the latest of several failures in the past few years, one of the more notable ones being Moscow's surprise annexation of Ukraine's Crimean region last year. China was also able to rapidly increase its territorial island-building in the South China Sea without much notice.

One senior administration official speaking to Reuters insisted there were "no surprises" and that lawmakers were "comfortable" with the intelligence they received leading up the Russian intervention.

Other officials said intelligence agencies are attempting to ramp up their spying efforts on Russia but do not have adequate resources due to much of it being allocated to counterterrorism efforts in the Middle East.