Zebari was commenting on a report in "The New York Times" saying debate was growing in the administration of U.S. President George W. Bush about a gradual drawdown of forces.
"This could produce a civil war, partition of the country and a regional war," Zebari told a news conference. "We might see the country collapse."
Responding to the newspaper report, the White House denied it was considering a troop withdrawal based on a political judgment.
"Withdrawing our troops prematurely based on politics, not on the advice of our military commanders, would not be in our national interest," said White House spokesman Tony Snow, quoting remarks Bush made last week. "It would hand the enemy a victory and put America's security at risk, and that's something we're not going to do."
Bush is facing pressure in Congress over Iraq as growing numbers of lawmakers from his own Republican Party join opposition Democrats in calling for a withdrawal of U.S. troops.
More than 330 U.S. soldiers were killed in Iraq from April to June, making it the deadliest quarter for U.S. troops since the March 2003 invasion.
Sunni Arab Vice President Tariq al-Hashimi said he would "be happy" to see U.S. troops leave now. But in remarks to Reuters, he asked, "Who will fill the security vacuum if these forces withdraw?"