America’s “biggest problem” in Syria is its regional allies, Biden told students at the John F. Kennedy Jr. Forum at the Institute of Politics at Harvard University on Thursday.

“Our allies in the region were our largest problem in Syria,” he said, explaining that Turkey, Saudi Arabia and the UAE were “so determined to take down Assad,” that in a sense they started a “proxy Sunni-Shia war” by pouring “hundreds of millions of dollars and tens of thousands of tons of weapons” towards anyone who would fight against Assad.

“And we could not convince our colleagues to stop supplying them,” said Biden, thus disassociating the US from unleashing the civil war in Syria.

“The outcome of such a policy now is more visible,” he said, as it turned out they supplied extremists from Al-Nusra Front and Al-Qaeda.

All of a sudden the regional powers that sponsored anti-Assad rebels awakened to the dawn of a major international security threat in the face of ISIS – now called Islamic State. After being essentially thrown out of Iraq it found open space and territory in eastern Syria and established close ties with the Al-Nusra Front which the US had earlier declared a terrorist group.

Now Washington needs a coalition of Sunni states to fight the Islamic State because “America can't once again go in to Muslim nation and be the aggressor, it has to be led by Sunnis, to attack a Sunni organization [the IS],” Biden said, acknowledging that it is for the first time that the US uses a geopolitical strategy.

“Even if we wanted it to be, it cannot be our fight alone,” Biden said. “This cannot be turned into a US ground war against another Arab nation in the Middle East.”