In December, civilians and soldiers signed a framework agreement, applauded by the United Nations, the African Union and several countries, but it still remains general with only a few deadlines set. Sudan has been plunged into turmoil since a 2021 coup led by army chief Abdel Fattah al-Burhan.
"It is important to note that the process remains open for them to come in," ambassador John Godfrey told AFP on Thursday, referring to key factions which refused to sign the agreement.
While the accord drew some international acclaim, opponents at home eyed it with skepticism, saying it falls short on specifics and timelines.
Former rebel leader Mini Minnawi, governor of the restive Darfur region, slammed the deal as "exclusionary."
Finance Minister Gibril Ibrahim, also an ex-rebel leader who had signed a peace deal with Sudan's short-lived transitional government, said it was "far from a national accord and does not lead to free and fair elections."
Godfrey spoke at the conclusion of the first round of talks in Khartoum over the second phase of the political process, focused mainly on neutering the remnants of long-time autocrat Omar al-Bashir's regime, ousted in 2019 in the face of mass protests.
Another round of talks is expected in the coming weeks over key contentious issues including transitional justice, accountability and security reforms.
Following the 2021 coup, the United States suspended $700 million in aid, but Godfrey said it has continued to provide "humanitarian" and "some development assistance."
"We have made it clear that until a new civilian-led government is in place in Sudan, we will not be in a position to restore the other lines of assistance," he said.
The United Nations said the talks this week mark "another important step towards realizing the aspirations of the Sudanese people for democracy, peace and sustainable development."
Godfrey expressed high hopes, saying it was "very clear" that negotiators were working towards restoring Sudan's transition.
Burhan has pledged the military would no longer be involved in politics once a civilian government is installed. The army chief has also expressed hope that international aid suspended since the coup would be restored.
In August, Godfrey took the post as the first U.S. ambassador to Sudan in nearly 25 years.