Egyptian Bedouin in the Sinai kidnapped two Brazilian women tourists on Sunday in the third such abduction in the peninsula this year, security officials said.
A Brazilian Foreign Ministry official in Brasilia said negotiations were underway under the auspices of the Egyptian Interior Ministry and that diplomats at the Brazilian embassy in Cairo were "working to find a solution."
The tourists were returning from a visit to the historic monastery of St Catherine in southern Sinai when the tribesmen seized them and an Egyptian tour guide, the Egyptian officials said.
They gave conflicting accounts of the tourists' ages. They had earlier said both were teenagers, but a police official said one was 18 and the other 40 years old.
A police official said one of the kidnappers was the father of a man sentenced to prison on drugs and weapons charges, and that he wanted his son's release.
The two armed Bedouin stopped a tour bus containing 38 tourists and abducted the two women and a guide at gunpoint, before driving off with them towards the peninsula's mountains, another police official said.
The incident marked the third kidnapping of foreign tourists in two months in the Sinai.
In February, Bedouin demanding the release of jailed tribesmen kidnapped three South Korean tourists in the same area, shortly after the abduction of two American women and their Egyptian tour guide.
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The tourists and the guide were all released quickly and unharmed, as were 25 Chinese workers seized at the end of January.
The sparsely populated region is where Egypt's most lucrative tourist resorts are located, as well as being home to a mostly poor and disaffected Bedouin population.
Since an uprising overthrew president Hosni Mubarak last year, the Sinai has grown even more lawless, with attacks on police stations and almost monthly bombings targeting a pipeline that exports gas to neighbouring Israel.
The Bedouin have pressed hard for the release of captive tribesmen they say have been sentenced unfairly on charges ranging from terrorism to drugs dealing.
On Friday, dozens of heavily armed tribesmen agreed to end an eight-day long siege of an international peacekeepers' camp in the north of the peninsula after the military promised to look into their demand.
The Bedouin said they would give the military a month to meet their demand for the release of jailed tribesmen, some convicted on terror charges. None of the peacekeepers, tasked with monitoring a treaty with Israel, was harmed.
Egypt's military, in power since Mubarak's ouster, tried to quell Islamist radicals in the peninsula with limited success last year, and the authorities now appear to prefer negotiating with armed tribesmen.
The military has already pardoned 18 Bedouin outlaws sentenced by military tribunals in absentia, while a state security court ordered a new trial for five Bedouin accused of deadly bombings in two Sinai tourist resorts in 2004.