Retired Gen. David Petraeus called Syria a "geopolitical Chernobyl" Tuesday during his testimony before the Senate Armed Services Committee.

Petraeus, the four-star general who led the "surge" in Iraq and revolutionized America’s approach to counterinsurgency, said Syria is a hotbed for "instability and extremism" that is now radiating across the Middle East.

He responded to the State Department’s relentless insistence that the solution in Syria will be a political transition, saying that military backing is necessary even for a political settlement.

"In every case, if there is to be any hope of a political settlement, a certain military and security context is required, and that context will not materialize on its own. We and our partners need to facilitate it," he said.

Petraeus emphasized the threat that Syrian President Bashar Al-Assad poses to the Syrian people, to the Middle East, and to America’s attempt to stabilize the region. He said American "inaction"–in the form of coalescing with Assad or rejecting a military context—could "carry profound risks and costs for our national security."

While Russian officials evoke the common threat that Islamic State poses in order to justify cooperation with the Assad regime, Petraeus said that Assad himself has been the "primary source of civilian casualties" as well as "a principal driver of the radicalization fueling IS and the refugee crisis."

In order to change the momentum in Syria, he said that the U.S. must develop "capable, moderate Sunni Arab ground forces" because they are "critical for any objective one might have in Syria." Developing opposition forces on the ground requires U.S. commitment "to protect them [Sunni Arabs] and the broader Syrian population against all enemies, not just ISIS."

Petraeus said that the U.S. must show that it "is willing to stand against Assad." This would include taking a strong stance against Russia in order to prevent being pushed "into a coalition with Assad, which appears to be President Putin’s intention."

While America "should not rush to oust Assad without an understanding of what will follow him," Petraeus said that "Assad cannot be part of the solution in Syria" since he is "responsible for the deaths of some 250,000 Syrians, the displacement of well over a third of Syria’s population, and the destruction of many of Syria's once thriving communities."