The vote "will be a new test of maturity for the people" of Guinea-Bissau, interim President Henrique Rosa said Friday.

"These elections must celebrate democracy," he said, adding: "We expect from the candidates a clear and firm contribution that honours our people, its political class and its institutions."

As the country geared up for the three week long campaign, authorities continued to round-up military officers accused of taking part in Yala's pre-dawn raid of the presidential palace earlier this week.

An interior ministry source told AFP on condition of anonymity that 58 soldiers had been detained so far.

Prosecutors also opened a criminal investigation against Yala for trespassing on the presidential grounds on Wednesday and for earlier statements claiming he was still the legal president, according to a copy of a prosecutorial document obtained by AFP.

Yala, bounced from office in a September 2003 bloodless coup, provoked a firestorm of concern with a May 15 announcement that his ouster was illegal and that he remained head of state in the coup-prone country.

He backed that announcement with a short-lived occupation of the presidential palace on Wednesday, accompanied by a sizable military presence, that ended without incident.

Yala has since backtracked from statements that the June polls should be voided, and said Thursday that he remained a candidate to succeed Rosa.

The ex-philosophy professor is one of 17 people approved by the Supreme Court to stand in the polls, along with former president Jose Bernardo Viera, despite bans on political activity by both of the deposed heads of state.

Electoral commission president El Hadji Malam Mane told AFP that the commission had "sufficient" funds to launch the campaign for the tiny country of 1.5 million people, in which some 540,000 people are registered to vote.

The European Union announced a 1.5 million-euro contribution to the running of the polls and has already sent several dozen elections observers to monitor the polls. A total 86 EU observers are expected to fan out around the country in the lead-up to the elections.

Police were interrogating soldiers of all ranks on Friday accused of involvement in Wednesday morning's raid, as well as key members of Yala's Social Renewal Party the interior ministry source said.

"Other arrests will likely follow," the source added.

Among those in police custody were General Nhare Yala, head of the presidential guard that allowed Yala and his soldiers to enter early Wednesday morning.

Regional leaders, fearing further uproar in Guinea-Bissau that could bleed over its borders into Senegal's fragile Casamance or into neighbor Guinea, swiftly condemned the pre-dawn raid as an attempted coup.

Guinea-Bissau gained independence from Portugal in 1974.