All the BBC's websites were unavailable early on Thursday morning because of a large web attack.

The problems began about 0700 GMT and meant visitors to the site saw an error message rather than webpages.

Sources within the BBC said the sites were offline thanks to what is known as a "distributed denial of service" attack.

An earlier statement tweeted by the BBC laid the blame for problems on a "technical issue".

In the message the corporation said it was aware of the ongoing trouble and was working to fix it so sites, services and pages were reachable again.

At midday it released another statement saying that the BBC website was now "operating normally".

"We apologise for any inconvenience you may have experienced," it said.

Attack traffic

It has now emerged that a web attack technique known as a "distributed denial of service" was causing the patchy response. This aims to knock a site offline by swamping it with more traffic than it can handle.

The attack on the BBC hit the main website as well as associated services including the main iPlayer catch-up service and iPlayer Radio app which were also not working properly.

The BBC has yet to confirm or deny that such an attack was responsible for the problems.

Social media reaction to the trouble was swift. Many urged the BBC to get the site back up quickly and lamented how long it was taking to fix the technical troubles.

By 1030 GMT the site was largely working again though some pages and indexes took longer than normal to load.

The BBC's crop of websites have suffered other technical problems in the past. In July 2014, the iPlayer and many of its associated sites were offline for almost an entire weekend.

The fault was traced to a database that sits behind the catch-up TV service.