Skype users worldwide were unable to log in to their accounts on Thursday.

Complaints from users of Skype being down was made from the US and some parts of Europe via popular social networking site, Twitter. Users in the Middle East and Asia have not reported any problems.

We're having some problems with our sign in server, so you may not be able to sign in to the Skype application or to your account as normal. If you're already signed in to the Skype application on your computer or mobile phone, you should be able to call/IM/etc as normal, the company said in a blog post.

Our forums are experiencing heavy traffic and so access may be slower than usual. Apologies! For more updates, watch this space or follow @skype on Twitter.

Skype is one of the most popular voice communication services in the world and has more than 350 million registered users. It is a pioneer in voice communication over the internet.