German Foreign Minister Frank Walter Steinmeier described the airstrike on an aid convoy near Syria’s Aleppo as an act of terrorism and proposed a temporary no-fly zone over the country.
"This attack on the humanitarian convoy is a horrible act, a terrorist act that we condemn in the strongest terms," said Steinmeier.
"If the ceasefire is to have a chance at all, the only path leads towards the creation of a temporary but complete cessation of all military aircraft movements over Syria - at least for three, but even better for seven days."
Aircraft struck the aid convoy, belonging to the UN, near Aleppo on Monday and killed 20 people, according to the Red Cross.
The Syrian Observatory for Human Rights monitoring group said the attacks were carried out by either Russian or Syrian regime aircraft.
Russia denied responsibility in a statement issued following the incident. “The air forces of Russia and Syria did not conduct any strikes against the UN aid convoy in the southwestern outskirts of Aleppo," the statement said.
The UN has suspended all aid convoys to Syria following the incident which UN official Jens Laerke described as a "war crime".
The call for a no-fly zone by the German foreign minister was echoed by the US Secretary General John Kerry.
Kerry on Wednesday told the UN Security Council flights over opposition held territories in Syria should be banned to allow aid flow into the country.
"We must move forward to try to immediately ground all aircraft flying in those key areas in order to de-escalate the situation and give a chance for humanitarian assistance to flow unimpeded,” said Kerry.
However, his proposal included only the Russian and Syrian regime aircraft.
Kerry’s remark comes a day after Turkish President Recep Tayyip Erdoğan reiterated his call for cooperation on enforcing no-fly zones in Syria.
— Turkish Presidency (@trpresidency) 21 September 2016
Ankara has consistently defended the need for establishing safe areas and no-fly-zones in northern Syria long before Syrian refugees started knocking on Europe’s gates.
The call did not receive much attention from major western countries until large refugee flows began to reach the borders of western European countries.
Turkey says a safe zone in northern Syria is the solution to the continuing refugee crisis and the threat of DAESH attacks outside Syria and Iraq.
Refugees who stay in Turkey and neighbouring countries could be settled in the safe areas, Ankara indicated earlier.
Turkey launched Operation Euphrates Shield into Syria with opposition fighters from the Free Syrian Army (FSA) in August to eliminate DAESH from Turkey's southern border.
The operation liberated the Syrian town of Jarablus, one kilometre (0.6 miles) from the Turkish-Syrian border, which was held by DAESH for nearly two years.