A Dutch Catholic school called off a one-day trip to Paris for 400 students on Friday because of fears of an attack by ISIS terrorists in the French capital's metro, although French officials have cited no evidence of a specific threat. Reuters reported that the graduate students from the southern Dutch town of Etten-Leur had been set to leave on Friday but the school said in a statement that the trip had been cancelled as a precaution after media reports about possible militant violence in France. According the news agency, Iraqi Prime Minister Haidar al-Abadi said last month he had credible intelligence that networks affiliated with ISIS insurgents were plotting to strike U.S. and French subway trains. But senior U.S. officials and French security services said they had no evidence of a particular threat. "The chance that something happens to our students is low, but we are ultimately responsible," Peter van Heusden, head of Catholic school KSE, told Reuters. "Concerns were expressed by parents and teachers about the terrorist threat," he added. France and the Netherlands have joined the U.S.-led air strike campaign targeting ISIS, whose ultra-radical forces have captured large swathes of Iraq and Syria and slaughtered those who resist them. Dutch security officials said there was now a slightly higher risk of an attack against the Netherlands, although they kept the official threat level at one stage below the highest. Asked about the cancelled trip at a press briefing on Friday, Prime Minister Mark Rutte declined comment. He repeated statements from state authorities earlier this week who called on Dutch citizens to continue to go about their normal lives.