Russian pilots abducted in Sudan's Darfur region
Two Russian pilots have been kidnapped in Sudan's western Darfur region, the country's state-run Suna news agency has reported.
They work for Sudan's Badr Airlines and were abducted in the town of Nyala on Sunday afternoon.
Meanwhile, the foreign ministry says a female US aid worker, held for more than 100 days in Darfur, has been freed unharmed and is now in Nyala.
There has been a spate of abductions in the last year targeting foreigners.
Correspondents say that most kidnappings appear to be for money.
But the kidnappers said they had released Flavia Wagner, 35, who works for Samaritan's Purse, to the authorities in South Darfur without receiving a ransom.
"We are making demands of the government: we want hospitals and education. If these demands are met, these kidnappings will no longer happen," one of her alleged abductors, Abu Mohamed al-Semeh, told the Reuters news agency.
Ms Wagner had been seized on 18 May, along with two Sudanese colleagues, who were released a week later.
"We thank God that Flavia is safe and free," said Franklin Graham, president of the US aid group. "We appreciate the help of the government of Sudan and the United States government."
She is reported to be well.
Earlier this month, two Jordanians working with Darfur's international peace force were taken by unidentified gunmen, but were freed three days later.
South Darfur's governor said all police and security forces had been mobilised to find the kidnappers of the Russian pilots.
"For the moment we don't have any information, either on the kidnappers or the kidnapped," the AFP news agency quotes governor Abdel Hamid Kasha as saying.
Badr Airlines is a private air company based in Khartoum which operates cargo and passenger services for various humanitarian operations in Darfur.
According to Reuters, the UN and African Union peacekeepers are digging a trench around Nyala, Darfur's largest town, to prevent kidnappers entering the town.
Unrest and fighting has intensified in Darfur over the last few months after rebel Justice and Equality Movement rebels pulled out of peace talks with the government, accusing it of acting in bad faith.
The UN estimates the six-year conflict in Darfur has cost the lives of 300,000 people and driven a further 2.7m from their homes.
The government puts the death toll at 10,000 and has said the problems in Darfur have been exaggerated for political reasons.
Sudanese President Omar al-Bashir is wanted by the International Criminal Court (ICC) for alleged war crimes committed in Darfur - charges he strongly denies.