The cause of issuing travel alerts in Europe was

More governments have issued travel alerts about possible new terror attacks in Europe. Both Japan and Sweden have issued statements warning their citizens traveling in Europe of a heightened risk of attacks by al-Qaeda or its affiliated groups, echoing alerts at the weekend by the US and Britain.
    There are clearly heightened intelligence concerns about possible threats in Europe and yet no clear-cut evidence, at least publicly acknowledged, of any very specific or imminent plot. None of the countries had appeared to be the main focus of interest. Britain, France and Germany have raised their own security alerts within their borders, but then they are quite elevated anyway. A number of different strands appear to have come together. There are reports of intelligence from a German national of Afghan origin held in Afghanistan, talking of a scheme for simultaneous attacks in Britain, France and Germany. There has also been reporting of possible intercepted communications from the Pakistan tribal areas, hinting of a similar plot.