Two Spanish-speaking militants have appeared in the latest propaganda video attributed to the Islamic State group, as Spain mourns the deaths of 15 innocents in last week's Barcelona attacks.The IS fighters praised the attackers behind last Thursday's killings in a busy area of Barcelona, when men drove a van into crowds killing 13 people and injuring over 100.Another two people were also stabbed to death by the IS-linked militants in the latest terror attack in Europe.Wednesday's video - entitled "The Conquest of Barcelona - showed a bearded militant and a masked man speaking to the camera and telling Spain to expect more attacks."I ask Allah to accept our brothers from Barcelona. Our war against you will carry on until the end of the world," said one of the men.The militants urge supporters to "wage war wherever they are", and praised the men killed or arrested following Thursday's attack in Catalonia.They warn that more attacks will take place unless Spain withdraws from a US-led coalition against IS in Iraq and Syria.IS already claimed responsibility for the killings in Barcelona through its Amaq news agency.The new tactics of uncordinated killings by under-the-radar IS sympathisers has shocked Europe, which has witnessed stabbings, car rammings, and bombings by lone wolf and group attackers in recent months.Analysts say it also highlights the growing weakness of the group that is on the run - having lost its Iraqi "capital" Mosul and looking soon to be defeated in Raqqa, Syria - and relying on terror attacks.