Madagascar gvt flouts prisoner deal -- opposition

* Opposition says government breaks political prisoners deal

* Ravalomanana ally receives two-year suspended sentence

* Government says Maputo deal not ratified

By Alain Iloniaina

ANTANANARIVO, Sept 23 (Reuters) - A senior ally of Madagascar's ousted leader on Wednesday accused the government of breaking a deal signed in Mozambique last month on the release of political prisoners.

The Indian Ocean island's justice minister confirmed late on Tuesday that Manandafy Rakotonirina had been found guilty of threatening state security and usurping public office.

Critics of Africa's youngest leader, Andry Rajoelina, who toppled Ravalomanana in a March coup, say he is cracking down on key political opponents as he seeks to consolidate his internationally-ostracised government.

"This verdict does not respect the Maputo power-sharing deal's terms on the liberation of political detainees," Fetison Andrianirina, head of Ravalomanana's opposition movement, said.

"With this government, we don't know on which foot to dance," he told Reuters.

The world's fourth largest island -- endowed with oil, nickel, cobalt, uranium, gold and coal -- has been rocked by political instability since the beginning of the year, unnerving investors and sending growth towards negative territory.

Last month's initial power-sharing deal -- signed by Rajoelina, Ravalomanana and two former presidents -- called for the cancellation of all charges related to this year's crisis and the immediate release of all political detainees.

The exiled Ravalomanana appointed Rakotonirina prime minister in April as he tried to create a parallel government.

However, Rakotonirina was arrested later that month and placed under house arrest. He was released, pending his trial, to participate in the reconciliation talks.

The opposition has accused Rajoelina of cherry-picking clauses from Maputo accord which suit him while flouting others.

Justice Minister Christine Razanamahasoa said there had been no violation of the agreement because the deal has not yet been ratified by parliament -- which was suspended by Rajoelina when he took power in March.

"These people will benefit from this deal (Maputo) but before then the upper and lower chambers of parliament need to be established and the text ratified before it can take effect," she told Reuters.

Madagascar's leaders agreed in Maputo to form a unity government but they have failed to reach agreement on how to divvy up the key posts, including president and prime minister.

Rajoelina then unilaterally formed a government which the opposition, African nations and some foreign powers rejected.

Two other close political associates of Ravalomanana have been arrested within the last fortnight, while in July the government blamed the former leader's allies for a spate of failed bomb attacks in the capital Antananarivo. (Writing by Richard Lough; editing by David Clarke)