A U.S. envoy said on Tuesday that the United States will not remove Sudan from its State Sponsors of Terrorism list as border conflict is going on.

"We made it clear that we can't move forward, let's say, on the State Sponsors of Terrorism while this conflict is going on in Southern Kordofan and Blue Nile," said Princeton Lyman, the U.S. special envoy for Sudan.

He told reporters at a news briefing that bombing hit civilian areas "almost indiscriminately", with denial of humanitarian access to international agencies.

"And there's the need to get back to negotiations," he said. "All three of those are critical for us to be able to move forward and take up the issue of State Sponsors of Terrorism or other things on the roadmap."

"We've made that point quite, quite clear to the government of Khartoum," he added.

Fighting in Southern Kordofan first erupted in early June between the Sudanese army and fighters aligned to the Sudan People 's Liberation Army, which became the regular army of South Sudan after its independence, and spilled over into nearby Blue Nile state three months later.

The U.S. State Department put Sudan on its list of State Sponsors of Terrorism in 1993 and imposed sanctions, accusing Khartoum of sheltering local and international terrorists including Osama bin Laden, the leader of al-Qaeda.

The U.S. once promised normalized relations with Sudan in return for its full compliance in implementing the Comprehensive Peace Agreement inked in 2005 to end the two-decade civil war between Sudan and southern Sudan.

Under the pact, the south voted in a January referendum to break away from the north and won independence on July 9, but some thorny issues remain unresolved between them, including oil revenues and external debt sharing, border demarcation and the status of the oil-rich Abyei region.