Sudanese authorities have detained suspects in the killings of four Nigerian peacekeepers in Darfur, state radio said on Tuesday, after U.N. chief Ban Ki-moon urged swift justice in the case.

"The authorities arrested those who are involved in the attack on UNAMID (the U.N.-African Union Mission in Darfur) near El-Geneina, in West Darfur," Radio Omdurman reported in an SMS news alert which gave no more details.

Rebels in Sudan's South Kordofan said on Tuesday they acted in self-defense by firing artillery against the state capital, a rare barrage which the governor reported killed six people.

"They are provoking us," Arnu Ngutulu Lodi, spokesman for the Sudan People's Liberation Movement-North (SPLM-N), told AFP.

Five people were killed and more than 20 wounded on Monday when rebels shelled the capital of Sudan's South Kordofan state, official radio said, in a rare strike on the government-held town.

"Five people are martyred and 23 wounded because of the SPLM-North shelling of Kadugli," Radio Omdurman reported in an SMS news alert, which gave no source for the information.

A Sudanese military transport plane crashed in the desert outside the capital Khartoum on Sunday, killing some and injuring others, the army said.

"The pilot informed the airport that he had a problem with one of his engines," before the plane went down west of Jebel Aulia, Sawarmi Khaled Saad, the Sudanese army spokesman, told Agence France Presse.

The United States on Thursday denounced an attack on a U.N. patrol in Sudan, voicing concern that security in western Darfur was worsening and threatening the implementation of peace accords there.

"The United States is deeply concerned by the sharp deterioration in security in North Darfur and adjacent parts of Jebel Marra, Sudan," State Department spokeswoman Victoria Nuland said in a statement.

Sudan and South Sudan reached agreements on a demilitarized border zone and oil production but made limited progress on contested areas, their officials said late Wednesday.

"There is agreement on some areas," said South Sudan delegation spokesman Atif Kiir, while his Sudanese counterpart Badr el-din Abdullah Badr spoke of "progress on many issues," with both saying a deal would be inked Thursday.

Sudan and South Sudan leaders are edging close to signing a deal on festering disputes between the rival neighbors on the fourth day of a presidential summit, Ethiopian officials said Wednesday.

"The final result of the negotiation between the two Sudans is expected to be made public by a press conference," Ethiopia's foreign ministry said in a statement.

Canada closed its embassies in Cairo, Tripoli and Khartoum for the day Sunday as a safety precaution for staff and the buildings, in the wake of attacks on several diplomatic premises.

"We take the safety of our personnel and our missions overseas very seriously," Foreign Ministry official Rick Roth told Agence France Presse.

Sudanese President Omar al-Bashir, who is wanted by the International Criminal Court, held talks with Egypt's Mohammed Morsi in Cairo on Sunday, officials said.

Bashir was met at Cairo's airport by Vice President Mahmud Mekki, and arrived with a large delegation of ministers.

The United States on Saturday ordered non-essential diplomatic staff and their relatives to leave Sudan and Tunisia following violent anti-American protests, and warned U.S. citizens against travel to those countries.

Tunisia's Interior Ministry threatened to punish all those involved in Friday's U.S. embassy attack that left four people dead and 49 injured after extremist protesters angry over the amateur film made in the United States stormed the installation.