Three people have been killed and several more injured after a shooting on a tram in the Dutch city of Utrecht.
Police said they were investigating a "possible terrorist motive" after the attacker, a 37-year-old Turkish-born man, fired shots inside the tram before fleeing. A police search for the suspect continues.
However reports in the Netherlands and Turkey cast the terror link into doubt, with a suggestion the shooting was a family dispute.
The mayor of Utrecht, Jan van Zanen, said five passengers were injured, down from an earlier figure of nine, with three seriously hurt.
Officers have issued a public appeal for information relating to Gokmen Tanis in connection with the shooting.
Heavily armed anti-terror officers were seen gathering in front of an apartment block close to the tram stop where the shooting took place, however no arrests were made.
Dutch military police have been put on "extra alert" at airports and "vital buildings" and heavily armed officers were deployed to government offices in The Hague.
German police have also upped surveillance on the country's border with the Netherlands, with officers told to monitor not only major highways, but also minor crossings and railway routes.
Mark Rutte, the Dutch prime minister, said he was "deeply concerned" about the incident as he announced crisis talks chaired by the government.
Schools in the city were instructed to keep their doors closed, with the terror threat in the wider province of Utrecht raised to its highest level.
However there was some confusion later on Monday over whether the attack had a terrorism link, with the Algemeen Dagblad newspaper citing a witness who said the gunman had targeted one woman on the tram and then shot other people who had tried to help her.
Turkey's Anadolu news agency claimed the gunman fired shots at a relative on the tram "due to family reasons".
Police, paramedics and three air ambulances were quickly on the scene of the shooting at 10.45am on Monday.
Local broadcaster RTV Utrecht quoted an eyewitness as saying he had seen a woman lying on the ground amid some kind of confrontation. Several men ran away from the scene, the witness said.
A photo showed a body covered by a white sheet near the tram.
One woman was reportedly shot in the chest. It was not immediately clear the extent of the other victims' injuries.
Jan van Zanen, the mayor of Utrecht, described the shooting as a "horrible and radical incident in which victims have fallen".
He added: "Police and the public prosecutor are currently looking for the person or persons responsible for this incident.
"The most important thing at present is taking care of the wounded and investigating the circumstances of the incident. We do not exclude anything, not even a terrorist attack."
Jeremy Hunt, the British foreign secretary, described the incident as "hugely concerning" and said the UK "stands with the people of the Netherlands".
The incident took place close at the city's 24 Oktoberplein, a major junction and tram stop outside the city centre.
After the shooting, Dutch political parties halted campaigning ahead of a provincial election scheduled for Wednesday that will also determine the makeup of the parliament's upper house.
Utrecht, the fourth largest city in the Netherlands, has a large student population with the country's largest university and is around 20 minutes south of Amsterdam by train. Gun killings are rare in the city, as elsewhere in the Netherlands.
The incident comes after a lone gunman killed 50 people in mass shootings at two mosques in the city of Christchurch, New Zealand, last Friday.