"There is no other solution... for Egypt but dialogue, including all political forces. Otherwise there is great danger that more blood will spill... which indicates the danger of civil war," he said.
Westerwelle renewed an early call for "effective protection of the Christian community" after a rise in attacks in recent days.
He also held an "extensive" telephone conversation with his Egyptian counterpart Nabil Fahmy on Saturday in which he called for calm and moderation, according to a statement from the foreign ministry.
Qatar is a key supporter of Egypt's Muslim Brotherhood, whose protests against the overthrow of president Mohamed Morsi on July 3rd have turned deadly amid clashes with security forces.
"We in Qatar are extremely concerned about the high number of victims. We are devastated by the violence," Attiyah said.
He called for an "end to violence and dialogue between all parties" as well as the freedom of political prisoners.
At least 173 people have been killed in Egypt in the past 24 hours alone, bringing the death toll to more than 750 people since police cracked down on two camps of Morsi loyalists in the capital on Wednesday.