By Fumbuka Ng'wanakilala

DAR ES SALAAM (Reuters) - Tanzanian President Jakaya Kikwete has sacked four government ministers following accusations of abuses committed by security forces during a huge operation against wildlife poaching.

The dismissals, which did not affect the key finance and energy portfolios, come after reports of arbitrary murder, rape, torture and extortion of innocent civilians by members of the anti-poaching crackdown dubbed "Operesheni Tokomeza" ("Operation Destroy").

Kikwete dismissed Defense Minister Shamsi Vuai Nahodha, Home Affairs Minister Emmanuel Nchimbi, Tourism and Natural Resources Minister Khamis Kagasheki and Livestock Development Minister David Mathayo.

"The president has agreed to nullify the appointments of all four ministers," Prime Minister Mizengo Pinda announced in parliament late on Friday to applause from lawmakers.

"The anti-poaching operation had good intentions, but the reported murders, rapes and brutality are totally unacceptable."

The dismissals come after a parliamentary inquiry uncovered the murder of 13 civilians, arrests of over 1,000 people and other abuses by members of the operation, which included soldiers, policemen, game rangers and forestry officers.

Kikwete sacked six ministers last year, including holders of the finance and energy portfolios, due to growing public and opposition discontent over graft allegations.

Investors have long complained graft is one of the main reasons for the high cost of doing business in Tanzania, which has made big discoveries of natural gas off its southern coast.

The president's latest intervention against officials seen to be abusing their positions could further strengthen his hand ahead of parliamentary and presidential elections in 2015.

Analysts said Kikwete was expected to announce a wider cabinet reshuffle in the coming days following growing criticism of the performance of other key members of his government, with more ministers likely to lose their jobs.

"Kikwete may now take the opportunity to reshuffle the entire cabinet but the Minister for Energy and Minerals, Sospeter Muhongo remains safe," said Ahmed Salim, senior associate at consultancy Teneo Intelligence.

"The focus will now turn towards the prime minister ...who has also been criticized, with opposition party members calling for his removal."

A new wave of poaching is threatening elephant and rhino populations in east Africa's second-largest economy.

Pinda said wildlife poaching had reached an alarming point, with a recent census at one of the country's biggest wildlife parks, Selous Game Reserve, showing elephant populations had plummeted to just 13,000 from 55,000 previously.

The government's anti-poaching exercise was suspended in November after just one month of the massive operation following reports of shocking brutality against innocent civilians.

(Editing by George Obulutsa and Mike Collett-White)