Warnings mounted on Wednesday over potential terrorist attacks just two days before the start of Euro 2016, with France on high alert as it readies to host two 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 according to their location, the interior ministry said.

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 US 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.

The country has mobilised 90,000 security personnel to guard Euro 2016, including 13,000 private guards. 

Paris police chief Michel Cadot has said an extra 3,000 officers were being added to the 10,000 allotted for the capital.

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 the Islamic State group.

Experts said jihadists could aim for areas with minimal security protection during Euro 2016.

"You protect 1,000 targets, so it's the 1,001st target that will be hit," said Pascal Boniface, of the Institute for International and Strategic Relations in Paris.

 

- Transport woes -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 paralysed parts of the network for a week. 

Unions voted to continue the train strikes for an eighth day on Wednesday 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 they will receive little sympathy if they disrupt the tournament.

Labour 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.

Source :AFP