Sudan on Wednesday accused Israel of bombing a military factory and threatened retaliation after the attack that killed two people.

"We think Israel did the bombing," Culture and Information Minister Ahmed Bilal Osman told a news conference.

Sudanese rebels have shelled the capital of South Kordofan state for the second time this week, they said on Wednesday, but it was not immediately clear if there were casualties or damage.

"There is some shelling inside Kadugli. It was yesterday evening," Arnu Ngutulu Lodi, spokesman for the Sudan People's Liberation Movement-North (SPLM-N), told AFP.

South Sudan said Saturday it was cancelling planned face-to-face peace talks with Sudan after accusing Khartoum of launching a new air raid on its territory.

Sudan denied bombing its southern neighbor, saying it had only targeted Darfuri rebels inside its own territory.

More than 100 Sudanese lawyers in black legal gowns demonstrated on Thursday in defense of free speech, Agence France Presse reported, on the 13th day of unprecedented public protests.

"Demonstration is a constitutional right," said one of their banners, while another declared "Freedom of expression is a legal right."

South Sudan must stop arbitrary arrests and improve the "dire" conditions in its prisons, where a third of inmates are held on remand and some without having been charged, Human Rights Watch said Friday.

"Flawed processes, unlawful detentions, and dire conditions in South Sudan's prisons reflect the urgent need to improve the new nation's fledgling justice system," the New York-based group said in a report.

Sudanese rebels seized control of an area in war-ravaged eastern Darfur after deadly clashes with government militias, their spokesman said on Saturday, adding that the army continued to bombard the area.

"Justice and Equality Movement forces seized the Um Ajajah region in eastern Darfur on Friday, destroying a mobile contingent of government militias and capturing 20 small vehicles and large trucks loaded with military equipment," JEM spokesman Gibril Adam Bilal said.

Arab League chief Nabil al-Arabi will travel to Sudan on Sunday, following a request from Khartoum for help over South Sudan's invasion of the Heglig oilfield, Arabi's deputy said.

Arabi will hold talks with President Omar al-Bashir and senior Sudanese officials, deputy Arab League chief Ahmed Ben Hilli told reporters.

South Sudan is ready to resume negotiations with Sudan, Juba's lead negotiator said late Tuesday on the eve of a United Nations date to restart talks, but also accused Khartoum of not being willing to meet.

"As per the timeline set out in the U.N. Security Council resolution, the parties are supposed to have resumed negotiations by the 16th of May, and we have not received any invite," negotiator Pagan Amum told AFP.

The first group of ethnic South Sudanese among up to 15,000 camped in crowded conditions in Sudan were to begin their journey home on Saturday, the International Organization for Migration said.

About 400 people will be brought to Khartoum by bus from the way-station of Kosti, about 300 kilometers (190 miles) south of the capital, ahead of a major airlift early on Sunday, IOM Sudan chief Jill Helke said.

South Sudan's president would cut short his visit to China due to "domestic issues", a Chinese official said Wednesday, as violence between the world's newest nation and Sudan intensified.

The curtailment of South Sudan President Salva Kiir's visit to China was confirmed by Wu Bangguo, nominally the second-ranking Chinese leader, during a meeting between the two men in Beijing.