Islamic State crisis: What is significance of strikes on IS?

The BBC's Bridget Kendall reports on the significance of the US and Arab nations joining forces to carry out air strikes on Islamic State (IS) targets in Syria.

US President Barack Obama has hailed the support of ''friends and partners'' Saudi Arabia, United Arab Emirates, Jordan, Bahrain and Qatar in the operation.

Activists say at least 70 IS militants and 50 other al-Qaeda-linked fighters were killed.