By Ben Hirschler

LONDON, July 9 (Reuters) - U.S. drugmaker AbbVie has been forced to retract comments by its chief executive about shareholder support for its bid for Shire after being caught out by British takeover rules.

Chief Executive Richard Gonzalez told Reuters in an interview on Tuesday he believed major Shire investors were "generally supportive of this transaction" - a comment he repeated in conversations with other media.

Under UK Takeover Panel rules a company attempting to acquire a rival is not allowed to claim support for its bid unless it has this in writing from shareholders.

"AbbVie confirms that it has not received any written commitments of support and accordingly retracts the statements," it said on Wednesday.

The error is a further example of the strict nature of British takeover rules, which also caused problems for Pfizer during its unsuccessful bid for AstraZeneca earlier this year.

AbbVie raised its offer for Shire to 30.1 billion pounds ($51.3 billion) on Tuesday, hoping to win over its reluctant target after three earlier offers were rejected.

(Editing by Mark Potter)