Secretary of State John Kerry re-stated his belief Monday that Syrian President Bashar al-Assad was behind a chemical weapons attack against rebel forces on the outskirts of Damascus last month, and said that the Syrian leader could prevent a strike against his country by U.S. forces if he turned over all his chemical weapons to the international community.

Kerry was speaking at a joint press conference in London with British Foreign Secretary William Hague. It was Kerry's last stop on a whirlwind European trip before he was scheduled to fly back to Washington Monday afternoon to brief Congress on the developing Syria situation.

"Sure, he could turn over every single bit of his chemical weapons to the international community in the next week - turn it over, all of it without delay and allow the full and total accounting, but he isn't about to do it and it can't be done," Kerry said in response to a question asking if there was anything Assad could do to prevent American action.

Kerry seemed to dismiss reports attributed to German intelligence that the August 21 attack could have been carried out with Assad's knowledge, telling the press that control over the use of chemical weapons is restricted to the Syrian President himself; his brother Maher al-Assad, a brigadier general in the Syrian Arab Army, and another general, whom Kerry did not name.

"We know that his regime gave orders to prepare for a chemical attack. We know they deployed forces," Kerry said. He added that the United States knows "where the rockets came from and where they landed ... and it was no accident that they all came from regime-controlled territory and all landed" in opposition-held territory.

"So the evidence is powerful and the question for all of us is what are we going to do about it? Turn our backs? Have a moment of silence?" Kerry said.

Pressed further on Assad's denials of responsibility made to a CBS reporter Sunday, Kerry said, "I just answered that. I just gave you real evidence. Evidence that as a former prosecutor in the United States I could take into a courtroom and get admitted."

Assad has denied responsibility for the attack, blaming it on the rebel forces he has been fighting in a bloody civil war that has cost over 100,000 lives since its beginning in March 2011.

The Associated Press contributed to this report