The U.S. Treasury Department said it targeted two companies linked to the army, including the country's largest defence enterprise, and two companies tied to the rival paramilitary Rapid Support Forces, including one involved in gold mining.

"We will not hesitate to take additional steps if the parties continue to destroy their country," a senior U.S. administration official, who briefed reporters on condition of anonymity, said.

"The targeting of the companies is far from symbolic," the official said, adding that the measures are intended to choke off the parties' access to weapons and resources that allow them to perpetuate the conflict.

Sudan's army and the RSF did not immediately respond to requests for comment.

The conflict, which broke out on April 15, has killed hundreds, forced more than 1.6 million to flee and turned the three cities that make up the capital around the confluence of the Nile - Khartoum, Omdurman and Bahri - into a war zone.

Residents said heavy artillery fire could be heard in northern Omdurman and intermittent firing in southern Bahri, despite a deal for a ceasefire that is meant to run till Saturday evening.

"We are being terrorized by the sounds of heavy artillery around us. The house has been shaking," 49-year-old Nadir Ahmed said in the Thawra neighbourhood of Omdurman. "Where is this ceasefire we hear about?"

Clashes also continued near a market in southern Khartoum, where at least 19 people were killed and 106 wounded on Wednesday, according to a member of a local neighbourhood committee.

SANCTIONS, WARNINGS

The United States, alongside Saudi Arabia, has been leading efforts to try to secure an effective ceasefire at talks in Jeddah, though both sides have breached a string of truces.

Saudi Arabia and the U.S. said late on Thursday they were suspending the talks, a day after Sudan's army announced it was halting its participation.

The sanctions are the first punitive measures imposed under an executive order signed by U.S. President Joe Biden in May. They target Sudan's largest defence enterprise, Defence Industries System, which the Treasury said generates an estimated $2 billion in revenue and manufactures arms and other equipment for Sudan's army.

Arms company Giad, also known as Sudan Master Technology, was targeted as well.

On the RSF side, Washington imposed sanctions on Algunade, which it said was involved in gold mining and controlled by RSF Commander Mohamed Hamdan Dagalo and his brother, as well as Tradive General Trading L.L.C., which it said was a front company controlled by another brother and procured vehicles for the RSF.

The companies, all key to the business and procurement activities of both forces, could not immediately be reached for comment.

U.S. Secretary of State Antony Blinken said visa restrictions were imposed on individuals in Sudan, including officials from both the army and the RSF and leaders from the government of Omar al-Bashir, who was ousted four years ago. Those hit with visa restrictions were not named.

'WARNING SHOT'

Outside Khartoum, clashes have flared in major cities in the western region of Darfur. A regional rights group said at least 50 people had been killed in the last week in the westernmost city of El Geneina, which has been cut off from communications for more than 10 days.

In another Darfur city, Zalingei, it said the hospital and university were looted and people were being killed "randomly".

Some government officials have relocated to the army-controlled Red Sea coast city Port Sudan, which has also become a base for the United Nations, aid groups, and diplomats.

However, a curfew was declared in the city this week as the army warned of "sleeper cells". Residents say buses have been stopped from entering the city, which is a key evacuation point.

In El Obeid, a regional hub southwest of Khartoum the U.N. World Food Programme reported food was being looted. "Food for 4.4 million people is at stake," agency chief Cindy McCain said.

Army and RSF leaders had held top positions on Sudan's ruling council after toppling Bashir in 2019. They fell out over the chain of command and military restructuring under a planned transition to civilian rule.

Cameron Hudson, a former U.S. official now at the Centre for Strategic and International Studies in Washington, said the sanctions would have little impact on the parties' ability to continue to wage war and were unlikely to be enforced by Russia or the United Arab Emirates, which have ties to the RSF.

"It's hard to think this sanctions announcement is the thing that will dissuade entities already doing business with these corporations from continuing," Hudson said.

"This feels like more of a warning shot than a direct hit, which is odd given that we are long past the time when warning shots should be used."