The State Security Services (SSS), Nigeria's secret police, detained Gbenga Arulegba from private TV channel African Independent Television (AIT) for the second time in two weeks on Monday, the group said, quoting AIT executives.

"The charge stems from the June 13 broadcast of Arulegba's daily talk show, Focus Nigeria, in which he referred critically to President Olusegun Obasanjo's official jet," the Committee to Protect Journalists (CPJ) said late on Monday.

Moves against media houses have increased in frequency in the past few months and government opponents in Africa's most populous country accuse it of cracking down on critics ahead of next year's elections.

The SSS had arrested Arulegba on June 14 and released him a day later. He was re-arrested when he reported for a scheduled meeting with SSS officers, according to an AIT bureau chief quoted by the CPJ. The SSS could not be reached for comment.

Obasanjo's new jet has been the subject of controversy in recent weeks. Newspapers have published numerous articles speculating about how much it cost and whether it was needed.

"It's outrageous that political commentary would result in a journalist being thrown in jail," said Ann Cooper, executive director of New York-based CPJ.

"The State Security Service's treatment of our colleague is appalling, and Gbenga Arulegba should be released immediately."

Press freedom is better in Nigeria than in many other African countries and newspapers regularly criticise the government in vitriolic editorials.

However, the SSS has detained a number of journalists without reason and it is listed as a "predator of press freedom" by another journalists' rights group, Reporters Without Borders.

AIT Chairman Raymond Dokpesi has speculated that Arulegba may have fallen foul of the authorities because his programme played a part in turning public opinion against a change in the constitution to allow Obasanjo to stand for a third term.

The Senate defeated the attempt in May but the shockwaves are still reverberating across the country.