By Khalid Abdelaziz
DUBAI (Reuters) -Sporadic clashes between Sudan's army and a paramilitary force spilled over into Thursday, puncturing the relative calm in the capital Khartoum and raising the risk of a week-long truce deal crumbling as concerns grew over a humanitarian crisis.
The ceasefire, monitored by Saudi Arabia and the United States, was reached after five weeks of warfare in Khartoum and outbursts of fighting in other parts of Sudan, including the long-volatile western region of Darfur.
The fighting - centred on a power struggle between Sudan's army and the paramilitary Rapid Support Forces (RSF) - has worsened a humanitarian crisis, forced more than 1.3 million people to flee and threatened to destabilise a fragile region.
The U.S. State Department said the ceasefire monitoring mechanism on Sudan had detected possible breaches of the agreement on Wednesday, including observed use of artillery, military aircraft and drones.
Washington also warned that Russia's Wagner mercenary group has been supplying the RSF with surface-to-air missiles to fight Sudan’s army, saying it was "contributing to a prolonged armed conflict that only results in further chaos in the region."
The army relies on air power while the RSF has spread out and taken cover in Khartoum's streets.
It is unclear whether either side has gained an edge in recent weeks. Clashes between the rival factions broke out again on Thursday in Khartoum and neighbouring Omdurman, eyewitnesses said, as well as the strategic city of El Obeid to the southwest.
The health ministry said some 730 people had been killed and 5,454 injured, though the real number is likely much higher.
Militia were also besieging Zalingei, capital of Central Darfur State, U.N. Darfur coordinator Toby Harward said. Telecommunications have been cut off and gangs roaming the city on motorcycles have attacked hospitals, government and aid offices, banks and homes, he added.
The same has happened in the West Darfur State capital El Geneina, where residents have had communication cut off for days after as many as 510 people were killed.
FAILED CEASEFIRE
The ceasefire was agreed on Saturday following talks in Jeddah. Previous truces have failed to stop the fighting. In statements late on Wednesday, the army and RSF accused each other of violating the agreement and launching attacks.
Reuters could not confirm the battlefield accounts.
"We have continued to see violations of the ceasefire," State Department spokesperson Matt Miller said in a briefing, saying the breaches included observed use of artillery and military aircraft and drones, credible reports of air strikes and sustained fighting in the heart of the Khartoum industrial area, as well as clashes in Zalingei.
He said Washington was continuing to engage with both sides and pressing the parties on alleged violations.
"We retain our sanctions authority and if appropriate we will not hesitate to use that authority," Miller said.
World Food Programme Executive-Director Cindy McCain said there was a need for increased public and private sector funding for relief.
"In the meantime, the conflict has to stop and we need help from the world community to make just that happen, otherwise we are going to lose another generation of Sudanese," McCain told journalists in Berlin.
The conflict erupted in Khartoum in mid-April as plans for an internationally backed political transition toward free elections under a civilian government were set to be finalised.
U.N. humanitarian agency OCHA said agencies were ready to deliver aid to more than 4 million people, but bureaucratic blockages and security issues were hampering distribution.
Out of the 168 trucks ready to deliver assistance, just a small number were on the move from Port Sudan to Gadaref, Kassala and Al Gezira, an aid official told Reuters.
The International Committee of the Red Cross said in a statement that anaesthesia and antibiotics and other medical supplies it had donated were now being distributed to seven hospitals in Khartoum, where only 20% of facilities are functioning.
"Hospitals also urgently need water, electricity and a safe environment for their patients and staff. We appeal to the parties to respect the work of medical personnel. Lives depend on it," said ICRC Sudan head Alfonso Verdu Perez.
Many residents are struggling to survive as they face prolonged water and power cuts, a collapse of health services and widespread lawlessness and looting.
The International Organization for Migration says more than one million people have been displaced within Sudan and 319,000 have fled to neighbouring countries, some of which are similarly impoverished with a history of internal conflict.
(Khalid Abdelaziz reported from Dubai; additional reporting by Simon Lewis in Washington, Emma Farge in Geneva, Nafisa Eltahir and Aidan Lewis in Cairo; Writing by Michael Georgy; Editing by Simon Cameron-Moore, Andrew Heavens, Mark Heinrich, Sharon Singleton and Deepa Babington)