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ADDIS ABABA (AFP) - Two Swedish journalists arrested in Ethiopia appeared in court this week, but will remain in detention until September 14 while a police probe continues, a Swedish official said Friday.

"They have once again been kept in custody by the judge for another 28 days and that is to prolong the police investigation," Swedish foreign ministry spokesman Anders Jorle told AFP by phone from Stockholm.

Photographer Johan Persson and reporter Martin Schibbye appeared in court on Wednesday, but no formal charges have been levelled against them since their July 1 arrest in the town of Jijiga near the Somali border.

They were arrested while embedded with rebels of the Ogaden National Liberation Front, opposed to the Ethiopian government. Fighting broke out between the rebels and Ethiopian troops, killing 15 and injuring six, including the journalists.

Jorle said the journalists were detained because they refused to show their passports to a border guard when entering Ethiopia.

"They entered Ethiopia in an illegal way and (the authorities) are investigating other possible violations against Ethiopian law," Jorle said.

The journalists said they were not being mistreated and have had weekly contact with Swedish embassy staff in Addis Ababa, Jorle added.

Press freedom watchdog Committee to Protect Journalists condemned the arrests of the journalists last month and called for their release.

"These journalists should not be detained for seeking to cover an under-reported story," CPJ's Africa consultant Tom Rhodes said in a statement.

Ethiopia is one of Africa's most restrictive countries for media, according to the watchdog.

Earlier this year, two local journalists were arrested for suspected "terrorist activities" along with several opposition members.