Error running Timertask Javafx

Question

I am trying to perform a task every 1 minute. The task is executed but when it arrives at the right minute to perform the action of this exception:

java.lang.Illegalstateexception: Not on FX application thread; currentThread = Timer-0

In short, I have a method that takes system time and checks if it equals bank time, if the hours are equal an alert is displayed. It was all working before I put in Timertask, The Method alertaGeral(); is called and works since it is not with equal Hours, when the hours are equal the alert should be displayed but the error.

My method:

 private void executarTarefa() {
        //****INICIA A TAREFA ELE VERIFICA A CADA UM MINUTO****//  
        Platform.runLater(new Runnable() {
        @Override
        public void run() {
         SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy hh:mm");
        System.out.println("Iniciado!");

        Timer timer = null;
        if (timer == null) {
            timer = new Timer();
            TimerTask tarefa = new TimerTask() {
                @Override
                public void run() {
                    try {
                        alertaGeral();
                        System.out.println("Alertado..");
                        System.out.println(sdf.format(new Date()));

                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            };
            timer.scheduleAtFixedRate(tarefa, TEMPO, TEMPO);
        }

        }
   });

    }