Then-president Barack Obama eased the sanctions in January, but made their permanent lifting dependent on Khartoum's progress in five areas of concern.
Then-president Barack Obama eased the sanctions in January, but made their permanent lifting dependent on Khartoum's progress in five areas of concern during a six-month review period that ends on July 12.
These conditions -- known as the "five tracks" -- include improved access for aid groups, an end to support for rebels in neighbouring South Sudan, an end to hostilities in the conflict zones of Darfur, Blue Nile and South Kordofan, and counterterrorism cooperation with US intelligence agencies.
"I can say without much hesitation that, with the few exceptions, the advances on the five tracks have been positive," US charge d'affaires in Khartoum, Steven Koutsis, said.
"The few exceptions being... the implementation of humanitarian access is uneven... and that we want to see that the government begins to act more on moving towards a more permanent agreement with the opposition" on ending hostilities.
Koutsis was speaking after touring Darfur, which has been gripped by conflict since 2003 when ethnic minority rose up against the Arab-dominated government in Khartoum.
Koutsis travelled across vast stretches of the western region, which is as large as France, to make a first-hand assessment of security ahead of President Donald Trump's decision on the trade embargo next month.
While Khartoum has allowed more access to many parts of Darfur, there are some where restrictions remain, aid workers say.
Washington first imposed the sanctions in 1997 over Khartoum's alleged support for Islamist militant groups. Now slain Al-Qaeda leader Osama bin Laden was based in the Sudanese capital from 1992 to 1996.
Washington has kept the sanctions in place largely in response to the scorched-earth tactics that President Omar al-Bashir's regime has used against the rebels in Darfur.
At least 300,000 people have been killed and 2.5 million displaced in the region, the United Nations says.
Koutsis said it was highly unlikely that a permanent agreement to end hostilities would be signed before July 12, but said Khartoum had shown "extreme restraint" in responding to rebel attacks over the past year.
"The fundamental issue that we asked for in return for sanctions relief was to stop any offensive," Koutsis said in El Daien, the East Darfur state capital.
"We considered aerial bombardments as offensives, as an offensive act, not a defensive act in any way."
Previously, government forces would launch a "large offensive" against pro-rebel communities if the rebels looted a village or stole cattle, he said.
"We have not seen that this time, in the last one year," said Koutsis, whose assessment of Darfur is expected to guide Washington's decision on sanctions.
"We have seen that when the army does attack, they act with restraint... they stop when they achieve their objective, they do not continue.
"We have seen that the government has shown extreme restraint even in circumstances where they could have responded under the genus of self-defence."
However, an expected drawdown of the 17,000-strong United Nations and African Union peacekeeping force in Darfur threatens to unravel the fragile gains achieved so far, Koutsis said.
"The biggest concern I have is the pace that UNAMID will draw down requires that the government of Sudan step up and fill those gaps in issues of security and development assistance," he said.
"As we have seen it is not clear that the government is fully able at this point to do that."
Some think tanks have urged Washington to maintain the sanctions, accusing Khartoum of curbing freedom of speech, violating human rights and repressing Christians and other minority groups.
Koutsis said Washington was not blind to these issues and had "big differences" with Khartoum over them, although the two currently enjoyed a level of confidence that hadn't existed for 25 years.
But the purpose of the sanctions was to end Sudanese support for extremist groups and bring peace to Darfur, he said.
"None of these other issues were the point of sanctions, and none of these other issues, therefore, should be linked to the lifting of sanctions."
Koutsis said that overall the sanctions had worked.
"Yes, I can say with absolute certainty that Darfur today is more peaceful than it was a year ago," he said.
"That is not to say that the causes of Darfur have been fully addressed, not by a long shot."