Cuban President Raul Castro warned Saturday his country could remain estranged from the United States for decades if Washington does not drop political demands.

"If we really want to make progress in bilateral relations, we have to learn to respect each other's differences and get used to living peacefully with them. Otherwise, no. We are ready for another 55 years like this," Castro said at the legislature's closing session.

World leaders stepped up efforts Sunday to pull South Sudan back from the brink of all-out civil war, as fighting raged across the country including in a key oil-producing region.

Special envoys from the United States and Nigeria were flying into the capital Juba, following on from a mission by foreign ministers from east Africa and the Horn and after an appeal for an end to the violence from United Nations chief Ban Ki-moon.

Four North Africans held in a migrant center on the outskirts of Rome have sewn their lips together in protest at their lengthy detention, Italian news agency ANSA reported Sunday.

The men, aged between 20 and 30, used a thread from a blanket and a small needle to sew their mouths shut at the Ponte Galeria facility on Saturday. They are receiving medical care, ANSA said.

Pope Francis on Saturday paid a pre-Christmas visit to dozens of children at a Catholic pediatric hospital in Rome, observing a decades-old papal tradition.

Stopping in the hospital's chapel, the pope was given a basket containing handwritten messages from the children.

Technical talks between Iran and world powers on how to implement a landmark nuclear deal clinched last month are making progress, but slowly, a senior Iranian negotiator said Saturday.

The negotiations began Thursday in Geneva on the accord reached in the Swiss city that is aimed at buying time for a diplomatic solution to a decade-long standoff over Iran's nuclear drive.

Jamming the dusty roads in South Sudan's capital Juba, vehicles of every type surround the bus station, as people hunt desperately for transport to flee fearing rebel attacks on the city.

Trucks and pick-ups loaded with passengers -- mainly children, women and the elderly -- squeeze into every available space.

Britain, the United States and Libya issued a joint call Saturday for justice over the Lockerbie bombing as services were held to mark the 25th anniversary of the attack, which claimed 270 lives.

The three governments gave their "deepest condolences" to relatives of those who died when Pan Am Flight 103 blew up over the Scottish town of Lockerbie on December 21, 1988, en route from London to New York.

The U.S. Senate has urged Iran to free jailed members of the Bahai faith, raising human rights concerns as President Barack Obama pursues diplomacy to curtail Tehran's nuclear program.

In a resolution approved unanimously Friday amid a flurry of activity before a holiday break, the Senate called on Iran to free seven Bahai leaders among other detained members of the religion, including 12 educators.

A helicopter crash in central Switzerland on Saturday hurt the pilot and four other occupants -- but a seven-year-old child on board escaped uninjured, police said.

Two of the occupants -- the mother of the child and a flight assistant -- were severely hurt in the accident, which occurred as the 45-year-old pilot was attempting to land the helicopter in a parking lot on a military-owned field in the canton of Glaris.

NATO on Saturday opened negotiations with Afghanistan over a proposed military force to stay in the country after next year, but said no deal would be signed until after a separate agreement with the U.S. was completed.

Afghan President Hamid Karzai and the U.S. have been in a long and bitter stand-off over the bilateral security agreement (BSA), which would see several thousand U.S. troops deployed in Afghanistan after 2014.