Warnings increased Wednesday over potential terrorist attacks just two days before the start of Euro 2016, with France on high alert as it prepares to host 2 million foreign football fans.

The French government was set to launch a smartphone app which would warn visitors of any "major crisis," a day after Britain warned that fans could be targeted during the month-long tournament. The free application, available in English and French, would alert users to any suspected attack or other disaster based on their location, according to the Interior Ministry.

The British Foreign Office on Tuesday said there was a "high threat from terrorism" during the month-long championship. "During Euro 2016, stadiums, fan zones, venues broadcasting the tournament and transport hubs and links represent potential targets for terrorist attacks," the Foreign Office added.

The U.S. State Department gave a similar warning last week, saying that "unaffiliated entertainment venues broadcasting the tournament in France and across Europe" were also potential targets.The arrest of a Frenchman with an arsenal of weapons in Ukraine on Monday has heightened security fears. Ukraine said the 25-year-old, identified in France as Gregoire Moutaux, was planning to attack multiple locations including mosques and synagogues before and during the tournament. But France has made no official comment on the arrest and anti-terrorist prosecutors have not been assigned to the case, suggesting authorities do not believe there was any imminent threat to Euro 2016.Meanwhile, a YouGov survey has indicated that many Germans worry about this summer's Euro 2016 competition. Around 30 per cent of German respondents say they will avoid mass-viewing events this summer, preferring instead to watch the games at home or in smaller venues. Those who said that they were worried about terrorism added that they would also try to avoid public spaces during the games, which start on Friday and run through July 10. Of the respondents, 42 per cent said they saw increased danger of an attack during the games.The country has mobilized 90,000 security personnel to guard Euro 2016, including 13,000 private guards. Paris police Chief Michel Cadot said an extra 3,000 officers were being added to the 10,000 allotted for the capital.German federal police said their officers are being sent to France to help with security during the football tournament and will be able to carry their firearms. Federal Police spokeswoman Nicole Bellinghausen on Wednesday confirmed a report in Bild newspaper that in addition to their sidearms, the German police will also be able to carry pepper spray and other such weapons, but said it was not unusual for them to be armed while helping outside Germany.She would not say for tactical reasons how many German police would be sent to France for the month-long tournament, but said they would be deployed in several locations primarily to help deal with German-speaking fans.The country is still under a state of emergency following November's suicide bombings and shootings in Paris that left 130 people dead and were claimed by DAESH. On Tuesday, a senior counter-terrorism official told AFP that they remain deeply concerned that extremists could aim for areas with minimal security protection during Euro 2016. "From the point of view of preparation, we have done as much as possible," he told AFP on the condition of anonymity. He added, "to be totally honest, I am worried."Ahead of the opening match between the hosts and Romania on Friday, France also faces the threat of disruption to rail travel, due to strikes that have paralyzed parts of the network for a week.Unions voted to continue the train strikes for an eighth day yesterday, despite receiving an improved offer on pay and conditions from state-run operator SNCF in all-night talks. The rail strike was limited in scope on Tuesday, but even if trains return to normal, the threat of a walkout by Air France pilots still hangs over the four-yearly gathering of Europe's top football nations.The pilots are set to ground planes for four days from Saturday over pay, just when an estimated two million visitors will begin heading for France. French President Francois Hollande has warned the unions that they will receive little sympathy if they disrupt the tournament.Labor reforms introduced by Hollande's unpopular Socialist government have led to three months of strikes and sometimes violent protests. The reforms are designed to make it easier to hire and fire people, but opponents say they will erode job security.