As the United States nears the one-year anniversary of its fight against the Islamic State, the military efforts in Syria appear to be ramping up -- much to the dismay of Sen. Tim Kaine (D-VA).

Kaine joined HuffPost Live on Thursday and sounded off on the increasing military operations against the extremist group. While the senator said he is "supportive of U.S. military action against ISIL," he urged Congress to weigh in on the matter.

"I dont want it to be done on a presidential say-so without a vote of Congress. This is now basically an illegal war. I dont think theres a legal justification for it," Kaine told host Alyona Minkovski .

The Senate Foreign Relations Committee member went on to explain why the president's choice to act against ISIS without Congressional authorization could not be justified under the Constitution or the 2001 Authorization for Use of Military Force , which allows the president to take action against anyone connected to the September 11 attacks. Kaine said:

"The president can take unilateral action if the U.S. is under imminent threat of attack [and] thats not the case. So the Constitution doesnt allow the president to act unilaterally without Congress here. The president says that the authorization passed after 9/11 that said that the president could take action against the perpetrators of the 9/11 attacks covers this. Hold on a second! The perpetrators of the 9/11 attacks are Al-Qaeda. ISIL didnt form until 2003, and ISIL is battling Al-Qaeda in Syria right now. So the notion that theres any legal justification for this war without Congress weighing in, to me is ridiculous."

But Kaine didn't completely blame Obama for the "illegal" military action.

"The fault is on an overreaching president, in my view, but its even more on the shoulders of Congress, because Congress has affirmatively refused to debate or vote on this war, in deep derogation of its Constitutional responsibilities," he said. "But more importantly than that, its sending the message to the troops that Congress could care less. Thats also the message that ISIL gets -- Congress could care less. Its the message that other allies in the region get -- Congress could care less."

Watch the full HuffPost Live conversation with Sen. Tim Kaine here .

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