It's thought the attack could last several days.
Cameron & Sturgeon Lead St Andrew's Day Tributes
Political leaders have reflected on Scotland's contribution to the world as they marked the country's national day.
Prime Minister David Cameron used his St Andrew's Day message to say that Scotland "helps put the Great in Great Britain''.
In her special message, First Minister Nicola Sturgeon said that St Andrew - who spoke up for the under privileged - represents the kindness Scots show now to those who come to the country in search of peace.
She said: "St Andrew, who is renowned as the 'fisher of men', is a perfect embodiment of the warm welcome and kindness which we extend to all who come to Scotland.
"St Andrew spoke up for the less privileged. He was responsible for drawing attention to the existence of the loaves and fishes which eventually fed the 5,000. He championed the minority and saw that they were included.
"At this time, when the world is touched by terror and people are fleeing their homeland in search of peace, Scotland can draw from its patron saint and continues to be a place of safe haven.
"We are a nation which has welcomed and will continue to welcome many people from across the world over the years. From China to Poland, from Syria to India, people have brought their cultures and traditions to this country. Our communities have benefited and so has the richness of our lives, making Scotland the thriving country it is today.
"Let's use today, our national day, to reinforce that warm welcome.''
Mr Cameron hailed the contribution the country's people make to the UK and the rest of the world.
He said: "Whether it is the arts, sport, business, philanthropy or cutting-edge technology, you can bank on Scotland punching above its weight: taking on the world - and winning.
"In the last year alone, its people have helped free Sierra Leone from the grip of Ebola - like the remarkable Pauline Cafferkey.
"Our amazing GB Davis Cup team - led by the Murray brothers - played fantastic tennis in London and Glasgow.
"Ayrshire Dunlop Cheese received protected status - joining foods like Stornoway black pudding and Shetland lamb. The Forth Rail Bridge got world heritage status - the sixth site in Scotland to be recognised by Unesco.
"Glasgow once again showed the warmest of sporting welcomes - this time, to the World Gymnastics Championships. And world-class laboratories, ship yards and factories across the central belt made a vital contribution both to our economy and to our defence.
"Scotland is a constant source of pride and passion. It helps put the Great in Great Britain.
"That's why, during that tense match at Twickenham, the whole of the United Kingdom was willing on Greg Laidlaw and the entire Scottish rugby team.
"It's why the Saltire flies proudly around the world - and today, over Downing Street as well.''
Downing Street it set to host a special St Andrew's day reception this week, with guests including representatives from business, the arts, the armed forces, sports world and charity volunteers.
Sturgeon says Trump is on the "wrong side" of the debate.
The boys were found inside the Sainsbury's store at 2am on Tuesday.
The incident, which happened at Ibrox station, was reported to British Transport Police before 8pm on Saturday.
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