General John Allen, special presidential envoy for the US-led coalition fighting against ISIS, said in an interview with BBC that to end the refugee crisis facing Europe ISIS had to be defeated and Syrian President Bashar al Assad "had to go."
He also praised Iraq's Prime Minister Haider al Abadi as "a real partner" and said the coalition was in a stronger place than a year ago.
Europe has been facing a huge refugee influx from Syria, Iraq and other countries who are running away from violence and poverty in their hometowns.
Allen said, "The millions who are fleeing their homes, that's not just about Daesh [arabic name for ISIS], it's also about the conditions in the region, the horrendous conditions that are a direct result of Bashar al Assad and several years of the civil war."
When asked if he felt in charge of for those fleeing to Europe, the general answered, "I feel that we can help them. We have worked very hard to help in the humanitarian crisis in that region.
"We've got to solve the conflict though. The conflict has got to be solved at a political level and a global level."
Allen calling ISIS a "manifestation of an absence of hope for so many people" said, "We are going to see that the manifestation of that conflict will play out in a number of ways - right now it is playing out in this heart-wrenching vision of the people who are streaming out of the region.
"This instability has been created by Bashar al-Assad and that regime. He ultimately chose to make war on his own people. That ultimately created the crisis that we face today.So it's not just about dealing with Daesh, it's about creating the conditions that can put us on track for a political diplomatic solution as well."
"Bashar al-Assad has got to go. He is both a point and a representation of what has caused so much instability in the region and so many people to want to fight, to fight him and to fight each other," he added.
The general said ISIS was being pushed back on several fronts and progress had also been made on a political level in Iraq.
As US President Barack Obama called for formation of a broad international coalition to combat ISIS last September, there has been a lot of efforts to fight against the militant group.
However, ISIS militants have made gains in some areas, including at Ramadi which Iraq's government promised to retake in May, but so far they have only managed to encircle the city, and at Palmyra in Syria.
Russia positioning tanks at Syrian airfield
Russia has positioned about a half dozen tanks at an airfield at the centre of a military buildup in Syria, two US officials said on Monday.
Russian President Vladimir Putin has been Assad's political ally since the start of the Syrian conflict in 2011..
Moscow is also sending an advanced anti-aircraft missile system to Syria, two Western officials and a Russian source said, as part of what the West believes is stepped-up military support for embattled Assad.
The Western officials also cited the SA-22 system would be operated by Russian troops, rather than Syrians. The system was on its way to Syria but had not yet arrived.
Britain-based Syrian Observatory for Human Rights said on Sunday Russian forces are working to extend an airstrip near a military airport in Latakia province which is a stronghold of Assad.
Russian President Putin has been Assad's political ally since the start of the Syrian conflict three years ago.
While the Obama administration says the only way to resolve the Syrian refugee crisis is to end the war, Russia is increasing its support for Assad.
Russian Minister of Foreign Affairs Sergei Lavrov announced his country would continue to help the Assad regime in "its efforts to fight terrorism."
Lavrov also criticised the West for rejecting cooperation with Syrian regime forces in the fight against ISIS.
The civil war in Syria started with anti-government protests in 2011 and has so far caused 250.000 deaths.
The government has lost large swathes of territory to rebels including militant groups such as Al Qaeda’s Syrian affiliate Nusra Front and ISIS.
Washington says Russian aid to Assad is responsible for a lack of negotiations between rebels and the regime.