A Serbian police officer martyred a man who shot him in the neck with a crossbow in front of the Israeli embassy in Belgrade.
Police identified the assailant as being a "convert" to Islam, who was born in 1999 in the town of Mladenovac, some 50 kilometres (30 miles) from Belgrade.
The attack happened around 11:00 am (0900 GMT) on Saturday in the Serbian capital, when the attacker shot the officer who was on duty outside the Israeli embassy.
The policeman in self-defence opened fire from his gun at the attacker "who died as a result of his injuries", said Interior Minister Ivica Dacic.
Authorities said some arrests had been made for "preventive reasons" and a number of people known to the security services were suspected of being linked to the attack.
The arrested included a man from Belgrade who was already held two years ago for being the administrator of several militant internet sites that called for "jihad", or holy war, but was released from custody, Dacic said.
"It is suspected that he directly participated in the logistical support and organisation of this terrorist act."
Police also said they were carrying out searches in a number of locations.
"There are several more persons that we are looking for, certainly for one who is on the territory of Serbia," President Aleksandar Vucic told reporters after visiting the wounded officer.
The attacker and his associates were tracked by the authorities before Saturday's attack but there was not enough evidence to arrest them, he added.
The 34-year-old officer, who underwent surgery in hospital, was in his guard booth when the attack happened.
According to authorities, the assailant had moved to live in Novi Pazar, which is a historical and political centre of the Bosniak Muslim minority in Serbia, and a centre of Islam in the country.
Dacic told reporters that there were early indications connecting the attack with people suspected of being linked to the Wahhabi movement -- an ultra-conservative branch of Islam that dominates in Saudi Arabia.
He said that overall security had been stepped up in Belgrade while special prosecutors had taken over the case.
Serbian Prime Minister Milos Vucevic strongly condemned the act and said his country would firmly respond to the threat of terrorism and stressed Serbian citizens could "feel safe".
Meanwhile, Serbia's top Islamic cleric Senad Halitovic strongly condemned the attack and wished the wounded officer a quick recovery.
Israel's retaliatory offensive has killed at least 37,834 people, also mostly civilians, according to data from the health ministry in Hamas-run Gaza.