By MacDonald Dzirutwe

HARARE (Reuters) - Zimbabwean police arrested the editor of a private newspaper on Tuesday over a report that suggested army commanders loyal to President Robert Mugabe were not opposed to Prime Minister Morgan Tsvangirai winning elections expected this year.

The arrest is the latest sign of mounting political tension as a five-year coalition brokered between Mugabe and Tsvangirai after violent elections in 2008 comes to an end, paving the way towards polls in the second half of the year.

Dumisani Muleya, editor of the Zimbabwe Independent, had been charged with publishing falsehoods, an offence which carries a maximum 20-year jail term, his lawyer, Tawanda Zhuwarara, said.

Independent reporter Owen Gagare and a company official were charged with the same offence, Zhuwarara said. The three denied the charges before being released from Harare's main police station.

The army has publicly denied speaking to officials from Tsvangirai's Movement for Democratic Change (MDC) and police have said that journalists who repeat the allegation could fall foul of the southern African nation's tough media laws.

Tsvangirai has had a frosty relationship with military commanders who have said they will not salute a president who did not take part in Zimbabwe's 1970s independence war. Tsvangirai did not fight in the war.

In March, police arrested prominent human rights lawyer Beatrice Mtetwa and aides from Tsvangirai's office a day after Zimbabweans voted in a referendum for a new constitution curbing presidential powers.

That case raised concerns about a crackdown by Mugabe's security forces before elections. Mtetwa will face trial at the end of this month on charges of obstructing and insulting the police.

At the weekend, police arrested the leader of the MDC's youth wing and charged him with insulting Mugabe at a rally.

The constitution, which also expands civil liberties and media freedoms, is likely to pass through parliament this week, paving the way for elections in which Mugabe, 89, hopes to extend his three decades in power.

However, the International Crisis Group, a political think tank, said the "continued absence of conditions for peaceful and credible elections" meant it might be wiser to delay the vote until the atmosphere improved.

It also urged the Southern African Development Community to keep the pressure on Mugabe to allow the reforms enshrined in the new constitution to be introduced.

"Deferral, if accompanied by firm SADC pressure, presents opportunities to promote reforms," the think tank argued in its latest country assessment.

(Reporting by MacDonald Dzirutwe; Editing by Ed Cropley and Alison Williams)