Two British tourists have died in Amsterdam after snorting what is believed to have been white heroin that was sold to them as cocaine.
The men, aged 20 and 21, and both from England, were found in a hotel room in the city yesterday next to traces of white powder.
A post-mortem examination is due to be conducted later this week to confirm the time and cause of the men's deaths.
The Foreign Office is liaising with Dutch authorities and is "providing consular assistance to the family", a spokesman said.
Saint Nicholas was welcomed by thousands as he arrived in the Netherlands this weekend, beginning the traditional run-up to Christmas there.
But there was controversy over his choice of companion. Instead of elves, Holland has a character called 'Black Pete' - a white man with a blacked face and curly wig.
Many believe there are racist overtones, and the event should be abolished.
Our Europe Correspondent Emma Murphy reports from Amsterdam.
Eurostar has reached an agreement to run direct train services between London and Amsterdam, the company announced.
Launching in December 2016, the journeys will take around four hours each way and will run twice a day, stopping at Antwerp, Rotterdam, Schiphol Airport and Amsterdam Centraal, Eurostar said.
“We have long been ambitious for expansion to new destinations so today’s announcement marks a major advance in our growth plans," said Eurostar chief executive Nicolas Petrovic.
"With over 3 million passengers travelling by air between London and Amsterdam, this is one of Europe’s most popular routes."
The city of Amsterdam is preparing for the swearing in of a new King today, as Queen Beatrix will officially abdicate from the throne.
Yesterday the Queen thanked the Dutch people in a final address before her abdication and urged them to support her son, Crown Prince Willem-Alexander.
A Vueling spokesman said there was no hijacking of a plane at Schiphol Airport, and blamed the incident on a communication problem between the pilot and control tower.
The Vueling plane was parked at a remote corner of Schiphol, away from the main terminal, surrounded by security personnel and several ambulances.
A notice on Schiphol airport's website says:
"During construction works this morning around the C-pier an airplane bomb from World War II was found. In the coming hours the bomb disposal unit will transport the bomb to an area outside of the airport facility and will attempt to defuse the bomb there.
"For the time being passengers should expect cancellations and delays."
Dutch police have confirmed that the Schiphol plane was not hijacked and that there was a mis-communication, according to Dutch news agency ANP.
Confusion over a possible hijacking arose because there was no radio contact, ANP reported citing the police.
Schiphol airport says police have boarded the plane to search the aircraft.
Michiel Hartzuikerfrom Dutch news agency NOS told ITV News that security forces were, "taking no risks" in their response after a plane landed in Schipol airport amid reports that there were hostages aboard.
Dutch media is reporting that that the passenger plane from Spain to Amsterdam was not hijacked, according to AP.