President Bashar al-Assad's veto-wielding ally Russian Federation says a ceasefire would be hard to achieve.
Planes have struck residential areas in the enclave of 400,000 people and, medical charities said, hit more than a dozen hospitals, making it near impossible to treat the wounded.
The German leader's comments came on the eve of the UN Security Council's expected meeting in NY to vote on a resolution calling for a 30-day ceasefire, the delivery of aid, and the evacuation of the wounded.
The Russian envoy to the UN, Vassily Nebenzia, told an emergency meeting of the security council on 22 February that Russia would not support the ceasefire resolution put forward by Sweden and Kuwait in its present form, calling it unrealistic.
The Gulf Arab state also stressed the need to allow access for humanitarian aid to reach the wounded to offer medical treatment and food.
Eastern Ghouta is the last rebel-held enclave bordering the Syrian capital, Damascus.
But Russia's United Nations ambassador, Vassily Nebenzia, put forward last-minute amendments, and said the proposed resolution was "simply unrealistic".
The recent escalation of fighting has killed at least 426 people and injured hundreds more, the Syrian Observatory for Human Rights monitoring group says. However, both have demanded discussion at Security Council.
"One has to ask where is Russian Federation, where is Iran, which had pledged in Astana to guarantee a ceasefire also in Eastern Ghouta", said Steffen Seibert, spokesman for Chancellor Angela Merkel, referring to peace talks in the Kazakh capital.
An UN resolution needs nine votes in favor and no vetoes by China, Russia, the United States, Britain or France.
On Thursday, the UN Security Council convened for an emergency meeting in NY to discuss to the situation in Syria and Eastern Ghouta, in particular.
It adds that foreign military forces should only operate in Syria "in coordination with official authorities", which several council diplomats - speaking on the condition of anonymity - described as unacceptable.
The vote on the resolution, scheduled for Friday morning was postponed twice and is expected to take place in the afternoon, Anatolio Ndong Mba, the permanent representative of Equatorial Guineau, an elected member of the Council, told reporters.