"Shocking news from London is a tragic confirmation that terrorists are on their bloody mission again. It also confirms the presence of the greatest global threat to the world today," Seks said in his message, adding that the attacks were a barbaric act directed at the civilised world, peace and democracy.
"Members of the Croatian Parliament unanimously and most harshly condemn today's terrorist attacks," Seks said.
"Please extend our sincere condolences to all members of the British Parliament and our full solidarity and support to citizens of London, particularly to the families and friends of the victims," the message said.
A series of blasts ripped through London during the rush hour on Thursday morning, killing at least 33 people and injuring dozens, according to police reports.
British Prime Minister Tony Blair said immediately after the blasts that it was quite clear that London was the target of a series of terrorist attacks.
Unnamed sources told the BBC that the al-Qaida terrorist network was responsible for the multiple attacks on London's transport system.