Washington's top diplomat in Iraq said Thursday that increased U.S. troop strength had brought down violence, but it was impossible to rush political reconciliation or to predict when conditions would allow the United States to begin reducing its involvement.

With less than two months remaining before Ambassador Ryan Crocker and Gen. David Petraeus, the U.S. commander in Iraq, were to report to Congress about progress in Iraq, the top envoy also told The Associated Press that political reconciliation was going to be "a long, hard pull."

"The surge (increase of 30,000 American troops) has done very well indeed in making a difference in security conditions. There's no question, in the Anbar (province) and Baghdad area. But it's not a light switch. You don't just flip something up and everyone is reconciled," Crocker said in an interview in his office in Saddam Hussein's Republican Palace.

Pressed repeatedly on when he thought U.S. troop levels could be reduced and other American involvement might be scaled back, Crocker said: "It's going to take longer than September."

The ambassador defended Iraqi Prime Minister Nouri al-Maliki, who is under heavy U.S. pressure for his failure to shepherd benchmark legislation through parliament, as being "as frustrated as anybody else here or at home.

"He would like to get things done and as he points out he understands the importance of the benchmarks for us. He'd like to get those done. ... The problems are immense. I do not think they are overwhelming unless we make them that or decide they are. But they do not admit of any quick or easy solutions," the sandy-haired Mideast diplomatic veteran said.

He warned those in the United States who are calling for a quick American withdrawal that he was not going to be able to give Congress positive answers about when U.S. troops could safely leave Iraq, which remains the world's most dangerous country in the fifth year of the U.S. military intervention.

He said he saw his mission as making "sure we're all looking at reality. I don't think any service is done either in Iraq or the U.S. by saying, again, 'It's going to be OK by November.' This is hard. There is tremendous damage that's been done physically, politically, socially and it's going to take time to repair."

Crocker said he felt his job, including the report to Congress by mid-September, was to ensure he presented "a sober look at what the consequences of other courses of action can be. Not to paint nightmare scenarios out of imagination, but just to think through what could happen should we decide we really don't want to carry forward any more."

He spoke of deep concerns about what would happen "if we decide based on reasons other than the conditions on ground in Iraq that we simply don't want to be involved any more. What that could mean in terms of Al Qaeda and insurgents? What that could mean in terms of a massive human catastrophe, with the bloodshed among the Iraqi civilians on scale we have not seen and may find hard to imagine?"

He concluded: "I think it is very important that for own interests that we stay with this until Iraq gets to the point of sustainable stability, I think that can be done."

A growing number of critics of continued U.S. involvement in Iraq disagree strongly, arguing that to stay longer damages American standing in the world, wastes taxpayer dollars, and sacrifices the lives of U.S. troops unnecessarily.

Complete coverage is available in FOXNews.com's Iraq center.