Brussels - The EU's diplomatic chief on Sunday expressed his deep concern over reports of violations of a ceasefire between warring neighbours Armenia and Azerbaijan in the disputed Nagorno-Karabakh region.

"We note with extreme concern the reports of continued military activities, including against civilian targets, as well as civilian casualties," EU foreign policy chief Josep Borrell said in a statement.

The EU's 27 member states "urge the sides to ensure full respect of the agreement on the ground," Borrell added. Borrell pushed the sides "to engage in substantive negotiations without delay under the auspices of the so-called "Minsk Group".This is a process that France, Russia and the US have led for decades to forge a lasting solution to the Karabakh conflict, but without success.The statement came after a ceasefire on Saturday was swiftly broken by more fighting, with both sides accusing the other of responsibility.