The EU official said he spoke to the Foreign Ministers of Armenia and Azerbaijan "to impress upon them that the ceasefire should be unconditional and strictly respected".
The fighting on the contact line in Nagorno-Karabakh have been ongoing since September 27, with Yerevan and Baku accusing each other of starting the firing.
An AFP team in the nearby city of Mingecevir, an hour's drive north of Ganja, heard the impact of a huge blast that shook buildings there at around the same time.
Azerbaijan claims to have made gains in Karabakh in recent days, with its defence ministry saying that 14 settlements have been taken as well as a strategically important plateau.