Security has been stepped up across Scotland's transport network after the terrorist attack on London as G8 leaders began meeting at Gleneagles.
An armed police officer stands guard outside the Gleneagles Hotel
Tony Blair left the G8 summit to assess the situation in London but returned to the talks on Thursday evening.
Mr Blair and other world leaders have condemned the attacks and pledged to continue with their summit in Scotland.
Officers with guns have been seen on the streets of Auchterarder since the blasts which killed at least 38 people.
British Transport Police said the explosions happened at Aldgate, Edgware Road, King's Cross, Old Street, Liverpool Street and Russell Square stations. One device went off on a bus.
About 1,000 Metropolitan Police officers had been deployed at Gleneagles.
A total of 252 specialist officers from the Met and the City of London Police were flown home during the day.
Mr Blair told journalists at Gleneagles: "It is the will of all the leaders of all the G8 that the meeting should continue in my absence and that we should continue to discuss the issues that we were going to discuss and reach the conclusions which we were going to reach.
"Each of the countries around the table have had some experience of the effects the terrorism and all the leaders, as they will indicate a little bit later, share our complete resolution to defeat this terrorism.
World leaders stand shoulder-to-shoulder with Tony Blair
"It's particularly barbaric that this has happened on a day when people are meeting to try to help the problems of poverty in Africa and the long term problems of climate change.
"It's also reasonably clear it is designed and aimed to coincide with the opening of the G8."
His words were echoed by President Bush, who said of those responsible: "They have such evil in their heart that they will take the lives of innocent folks. The war on terrorism is on.
"I was most impressed with the resolve of all the leaders in the room. Their resolve is as strong as my resolve."
A Tayside Police spokeswoman confirmed: "Security at government buildings, local airports, bus stations, train stations and ports has been heightened.
"There is no intelligence to suggest that the Tayside area will be targeted. This is a normal response to incidents of this nature and a step that will be taken by every police force in the UK."
Strathclyde Passenger Transport's commercial and production manager Liz Parkes said Glasgow's underground system was running as normal.
Glasgow's underground system is running as normal
She gave assurances that there was no specific threat to the underground but added that public confidence was vital and passengers were urged to be vigilant.
The city's underground security system was already "significant" because of the general heightened threat of terrorism.
Staff had also been extra watchful because of the G8 summit and the Special Olympics event being held in Glasgow.
She said: "Staff have been briefed and there are additional stewards on platforms.
Another SPT spokesperson, David McLavin said: "We have been advised by TranSec (the Government's Transport Security Directorate) that there is no heightened risk to Glasgow.
"However, we are making public announcements every 15 minutes to passengers and staff to be vigilant and look out for suspect packages.
"We are advising everyone not to over-react or panic because of events in London.
"We are also distributing TranSec advice to all staff and drivers."
Train operator GNER is advising passengers not to try travelling to London.
First Scotrail has cancelled all sleeper services to and from Euston station in London Glasgow, Edinburgh, Inverness, Aberdeen and Fort William because of security concerns.