BANGKOK, March 5 (Reuters) - Thai prosecutors on Thursday postponed a decision on whether to pursue lese-majeste charges against a supporter of ousted Prime Minister Thaksin Shinawatra for allegedly insulting the king in a speech in 2007.

Jakrapob Penkhair told Reuters the prosecutors had said they needed more time to check facts related to the case and would make a decision by April 29.

Jakrapob had to resign as a minister in a pro-Thaksin government in May 2008 when opponents stirred up controversy over his speech, which had been given to the Foreign Correspondents' Club of Thailand.

On Wednesday a group of rights activists and academics released a petition asking the Thai government to drop all current lese-majeste charges and reform the law.

They said the law had been abused for political gain and caused "heightened criticism of the monarchy and Thailand ... both inside and outside the country".

Lese-majeste, or insulting the monarchy, is a very serious offence in Thailand, where many people regard 81-year-old King Bhumibol Adulyadej as semi-divine.

It is punishable by up to 15 years in prison, although convictions, especially of foreigners, are rare and are normally followed quickly by a pardon.

Last month the king pardoned an Australian author jailed for three years after being found guilty of insulting the crown prince in a little-read novel.

Giles Ungpakorn, a prominent leftist commentator and an academic at Bangkok's Chulalongkorn University, was charged with lese-majeste in January and fled to Britain in February.

The Economist magazine has failed to appear in Thailand on several occasions since December because of articles about the king and the lese-majeste law.

(Reporting by Chalathip Thirasoonthrakul; Writing by Kittipong Soonprasert; Editing by Alan Raybould and Dean Yates)