A tribal clash has claimed many casualties near the tense undemarcated border between Sudan and South Sudan, a source familiar with the incident said on Tuesday.

The violence occurred between nomadic Arab Misseriya cattle herders and members of the South Sudanese-based Nuer tribe west of the disputed Abyei region, said the source, an Abyei resident.

The navies of Sudan and Saudi Arabia have launched their first joint military exercises in the Red Sea, Sudan's official SUNA news agency reported on Sunday.

The training is to run until Wednesday and focus on anti-smuggling operations and "boosting security and stability", SUNA quoted Sudan's military spokesman Sawarmi Khaled Saad as saying.

Britain called on Chad on Saturday to arrest Sudanese President Omar al-Bashir while he visits N'Djamena for a regional summit and to hand him over to the International Criminal Court.

Chad is one of the countries signed up to the ICC's founding treaty which are legally bound to arrest Bashir, who is wanted for war crimes, crimes against humanity and genocide in the long-running Darfur conflict.

The United States on Friday warned of a dangerous increase in tensions on the undemarcated border between Sudan and South Sudan after reports of clashes between the two sides.

Washington is "deeply concerned" by the reported incidents in disputed border areas between South Sudan's Upper Nile state and Sudan's Blue Nile, the U.S. embassy in Khartoum said.

Aid delivery is in jeopardy for an estimated 100,000 people affected by violence in Sudan's Darfur region unless authorities grant better access, the United Nations warned on Thursday.

One humanitarian agency has said the number of displaced people is the largest in recent years in Darfur, where a decade of civil war has been compounded by inter-Arab violence, banditry and tribal fighting.

Khartoum-backed militia in Sudan's South Kordofan state have killed 17 civilians, rebels said on Saturday, adding to tensions with South Sudan over a failure to implement security agreements.

The rebels accused a group of ethnic South Sudanese of ambushing a civilian lorry on Friday at Abu Nuwara, about 80 kilometers (50 miles) from the border with South Sudan's Upper Nile state.

Islamists fleeing advancing French forces in Mali have been spotted in Sudan's troubled Darfur region, a Sudanese rebel commander told Agence France Presse on Friday.

"We saw them," said Abdel Wahid Mohammed al-Nur, commander of a Sudan Liberation Army (SLA) faction which is fighting Khartoum's troops in Darfur.

The head of the Palestinian Islamic Jihad, accused by Israel of receiving arms which transit through Sudan, has met President Omar al-Bashir in Khartoum, official media reported.

Bashir discussed "issues of mutual concern" with Ramadan Abdullah Shallah during talks on Sunday at the presidential guest house, the state SUNA news agency said. It gave no further details.

The South Sudanese army on Sunday accused Sudan of launching a deadly air assault along their volatile border, but Khartoum promptly denied the claims.

A spokesman for the South Sudanese army (SPLA) said the attack occurred on its soil along the border in Upper Nile state.

Animal carcasses are rotting and tens of thousands of people have sought shelter in schools and government offices in Sudan's Darfur region after violence this month, the U.N. said on Thursday.

About 100,000 people are newly estimated to have been displaced or severely affected across a wide area of the Jebel Amir district of North Darfur state, the United Nations humanitarian agency (OCHA) said in its weekly bulletin.