Facebook Inc, the world's biggest social networking site, said its service was unavailable in some European countries on Wednesday morning because of technical problems.

Today we experienced technical difficulties causing the site to be unavailable for a number of users in Europe, Facebook said. The issue has been resolved and everyone should now have access to Facebook. We apologize for any inconvenience.

Some users turned to rival service Twitter to vent their frustrations at the outage, which appeared to last for about two hours according to postings.

Facebook, which has about 845 million active users worldwide, last month announced plans to raise $5 billion in an IPO expected to value the company at between $75 billion and $100 billion.

(Reporting by Paul Sandle; Editing by David Holmes)