After six months of civil war in South Sudan, the world's youngest nation is struggling with a worsening aid crisis and warnings of the risk of famine.

The conflict, which started in the capital Juba before spreading to other key states, has taken on an ethnic dimension, pitting President Salva Kiir's Dinka tribe against militia forces from rebel chief Riek Machar's Nuer people.

An Indian contractor with the UNAMID peacekeeping mission in Sudan's troubled Darfur region has been freed after 94 days in captivity, a statement said on Friday.

The African Union-United Nations Mission in Darfur said Irfan Jaffery, who was kidnapped on March 11, was released on Thursday in Kabkabiya.

Sudanese police on Friday detained four daughters of opposition leader Sadiq al-Mahdi as they violently broke up a protest demanding freedom for political prisoners, his party said.

"Police used violence and arrested 17 people including four daughters of Umma party leader Sadiq al-Mahdi," party secretary general Sarra Naqdallah told Agence France Presse.

U.S. Secretary of State John Kerry criticized Sudan on Thursday for sentencing a Christian woman to hang for apostasy, urging Khartoum to repeal its laws banning Muslims from converting.

Meriam Yahia Ibrahim Ishag, who was born to a Muslim father, was sentenced to death on May 15 under Islamic sharia law that has been in place since 1983 and outlaws conversions under pain of death.

The U.S. ambassador to the United Nations accused Sudan Thursday of intensifying attacks on civilians in South Kordofan and Blue Nile states, and of deliberately bombing schools and hospitals.

Samantha Power condemned "in the strongest possible terms" attacks she said were being carried out by the Sudanese government and its rapid support forces against ordinary people.

The heads of the EU's major institutions urged Sudanese authorities on Tuesday to free a Christian woman sentenced to hang for apostasy, joining a wave of international condemnation.

Jose Manuel Barroso, Herman Van Rompuy and Martin Schulz "express their deepest dismay and concern" over the fate of Meriam Yahia Ibrahim Ishag, who has been sentenced to a hundred lashes and sentenced to death by hanging on charges of apostasy and adultery.

A three-judge panel in Sudan will examine the appeal of a Christian woman sentenced to hang for apostasy, in a case that has drawn international condemnation, her lawyer said Monday.

"The judiciary appointed three judges last week to examine the appeal filed in the case of Meriam Yahia Ibrahim Ishag," lawyer Mohanad Mustafa told Agence France Presse, without specifying when they will deliver a ruling.

One person was killed Sunday in the Sudanese capital as police fired tear gas to disperse a demonstration over water shortages, police and witnesses said.

Hundreds of residents of southern Khartoum took to the streets after repeated cuts in drinking water supply to the area, blocking off a main road with rocks and tree branches, witnesses said.

Sudanese police on Sunday arrested an opposition leader accused of having criticized a counter-insurgency unit, an aide said, in the second such case in just over three weeks.

Sudanese Congress Party chief Ibrahim al-Sheikh was taken away from his home in Nuhud town of West Kordofan by police acting on an arrest warrant, the party's secretary general, Abdelqayum Awad, told Agence France Presse.

Sudanese troops on Friday captured a rebel position in South Kordofan, the military said Friday, as the United Nations voiced concern for civilians caught in fighting between the two sides.

"At noon today our armed forces liberated al-Atmur region, which is a military base... where the rebels stocked heavy weapons, including cannons and multiple rocket launchers," army spokesman Sawarmi Khaled Saad told Agence France Presse.