Oracle’s $7.4bn acquisition of Sun Microsystems hit an unexpected and potentially damaging obstacle in Brussels on Thursday as European antitrust officials opted to break with Washington in order to scrutinise the deal more closely.

The more stringent stance in Brussels breaks with recent efforts by competition authorities on either side of the Atlantic to align their investigations, and is particularly notable since the deal has already been given the green light by a new US administration that has taken a tougher line on competition issues, particularly in the tech industry.