Police forensic experts examine the scene of an explosion in Budapest that seriously wounded two police officers. EPA/PETER LAKATOS (Peter Lakatos/EPA)

Hungarian authorities staged a manhunt Sunday for the principal suspect in a bomb attack that seriously wounded two patrol officers late Saturday, with authorities saying the homemade device had been planted in an apparent attempt to target police.

The incident comes as countries across Europe are on edge following a series of attacks by suspects linked to or inspired by ­Islamist extremists, as well as an increasing number of acts of violence carried out by the far-right. National police chief Karoly Papp, however, said investigators had not been able to determine whether Saturday’s attack — near an empty storefront on a main artery in Budapest, the capital — was intended as an act of terrorism.

The explosion took place several blocks from one of Budapest’s main entertainment districts, which was not crowded at the time. The nature of the blast — a device armed with metal projectiles and detonated while two officers were on regular patrol — suggested an intent to strike at the city’s police, Papp said. Such an attack would be highly unusual in Hungary.

“The target was not one of the injured police officers but the police force” itself, he said. “I would like to make it clear that we will find the perpetrator.”

Authorities set up strict controls at airports and train stations in search of a suspect caught on security cameras. A 23-year-old female officer remained in critical condition on Sunday, while a 26-year-old male officer was stabilized after emergency surgery.

Officials released a recording of the male officer calling for assistance after the detonation sent shrapnel flying toward the street, blowing out storefront windows and cracking concrete.

“One policeman is unconscious, one policeman is unconscious. . . . Call the police, help, help, send the ambulance,” the officer is heard saying in the recording.

Investigators, Papp said, were analyzing images from 145 security cameras in the vicinity of the explosion. The suspect is believed to be a 20- to 25-year-old male wearing jeans and a light-colored fishing cap. Authorities were offering a reward of 10 million ­forints (about $36,700) for information on the suspect.

The attack came as Hungarians prepare to go to the polls next Sunday to vote in a referendum on a European migrant-quota system that would compel E.U. countries to take in more asylum seekers. The government of staunchly anti-migrant Prime Minister Viktor ­Orban is campaigning strongly against the measure, arguing that the mostly Muslim migrants pose a threat to Europe’s “Christian” identity and its security. Polls suggest the Hungarian public is likely to reject the quotas, although turnout must reach 50 percent for the vote to be considered valid.

Hungary has established itself as perhaps the least-welcoming country in the E.U. for refugees. Last year, it constructed a fence along its southern border to block migrants streaming into central Europe from the Middle East, a step that has reduced a flood of migrants transiting Hungary to a trickle. Hungary is now allowing in only 30 asylum seekers per day — compared with a peak of more than 13,000 per day last year.

Gergo Saling contributed to this report.