The highly-anticipated release of World of Warcraft: The Burning Crusade has been delayed until January 2007, game maker Blizzard has said.

Blizzard president and co-founder Mike Morhaime made the announcement in a press release on Thursday.

Mr Morhaime said the delay would allow Blizzard to "extend the closed beta test and further refine the new content that will ship with the game".

The California-based developer had originally planned to launch its expansion pack by the end of 2006.

"We appreciate the enthusiasm surrounding World of Warcraft: The Burning Crusade, and we're excited about putting the finishing touches on all of the new content," Mr Morhaime said in a statement.

He added: "We feel confident that the extra time spent polishing the game will result in the high-quality experience that our players expect and deserve."

The expansion will add new lands, quests, monsters, magic items, spells and abilities, two new player races, a new player profession and 10 new levels for players to achieve.

Mike Morhaime, Blizzard: "We feel confident that the extra time spent polishing the game will result in the high-quality experience that our players expect and deserve."

World of Warcraft, a massively multiplayer online role-playing game (MMORPG), was launched in the US, Australia and New Zealand in 2004.

The adventure game has since been released in multiple countries throughout Europe and Asia.

In April 2006, Blizzard announced that the game had reached six million subscribers worldwide.

Blizzard, a unit of French media company Vivendi SA, has yet to provide details of exact launch dates or pricing decisions for the expansion pack.