In pictures: Riyadh bomb blasts

1 of 8 A grim-faced Colin Powell visited one of the three sites hit by suicide bombers...

2 of 8 ... and told journalists that terrorism continued to be "a threat to the civilised world"

3 of 8 The bomb attacks - using cars packed with explosives - caused widespread destruction...

4 of 8 ... with dozens reported dead and several injured, including a young British girl...

5 of 8 ... and British schoolteacher Graham Bull

6 of 8 Multi-storey apartment blocks were gutted

7 of 8 The Saudi authorities have now sealed off the area

8 of 8 The US is sending investigators to help hunt for those responsible