Tighter security and ID checks have been introduced at Belgian train stations following a foiled terrorist attack on a train last week.
The UK Foreign Office warned there was a high threat from terrorism in the country. "Attacks could be indiscriminate, including on public transport and transport hubs and in places frequented by foreigners," it said.
It pointed out the Brussels hosts a number of international institutions, including EU and NATO buildings, which are sensitive locations.
"There is considered to be a heightened threat of terrorist attack globally against UK interests and British nationals, from groups or individuals motivated by the conflict in Iraq and Syria. You should be vigilant at this time," it added.
Last week’s incident took place on a Thalys train travelling from Amsterdam to Paris via Brussels when an attacker carrying a machine gun opened fire in a carriage before being wrestled to the ground by several passengers.
The attacker, 25-year-old Moroccan Ayoub El-Khazzani, claimed his motivation was robbery due to hunger but French police say his attack was premeditated and well-prepared and it is alleged he had watched a jihadist video on his phone shortly before opening fire on the train.
El-Khazzani was carrying 270 bullets for his assault rifle and a bottle of petrol. No-one died in the attack and one Briton and three Americans were awarded medals for their bravery in bringing him down.
