European competition regulators on Friday gave a cautious reaction to improved concessions offered by Lufthansa, as part of its effort to take over Austrian Airlines, meaning that completion of the deal remains uncertain.

The European Commission said that the new terms – which are designed to address the regulator’s worries about the amount of competition which would exist on routes between Vienna and a number of European cities – had been made in a letter from Lufthansa’s chairman on Thursday night.