The talks, sponsored by the United Nations and African Union, seek to break the country's political deadlock since military leaders seized power last October.
Talks aiming to restore political order in post-coup Sudan have begun with military leaders at the table and the main civilian groups boycotting.
"It is important to not let this moment slip", United Nations special representative Volker Perthes told reporters on Wednesday in Khartoum.
"We are asking everybody to work with one another in good faith".
Wednesday's talks were attended by military officials, representatives from several political parties, and senior members from ex-rebel groups.
But Sudan's main civilian bloc, the Forces for Freedom and Change (FFC) – which was ousted from power in the coup – as well as the influential Umma party have refused to take part.
Members from the resistance committees, informal groups which emerged during the 2019 protests against the then president Omar al Bashir and which have led calls for recent anti-coup rallies, were also absent.
The meeting "does not address the nature of the crisis" and any political process should work on "ending the coup and establishing a democratic civilian authority", the FFC said in a statement earlier this week.
The Umma Party said the objective of the talks was "undefined" and the political climate "was not fully prepared."
Sudan has been rocked by deepening unrest, near-weekly protests, a violent crackdown that has killed over 100 people and a tumbling economy since the October 25 power grab led by army chief Abdel Fattah al Burhan.
The military takeover derailed a fragile transition to civilian rule that had been established following the 2019 ouster of Bashir.
The UN, African Union and regional bloc IGAD have since March been pushing for Sudanese-led talks to break the political stalemate.
On Tuesday, Burhan hailed the talks as a "historic opportunity" and called on political factions "to not stand as a stumbling block".
Burhan last month lifted the state of emergency imposed since the coup, and authorities have in recent weeks released multiple civilian leaders and pro-democracy activists.
Perthes welcomed the measures, but said "more can be done".
IGAD envoy Ismail Wais urged absent factions to join the talks.
"They are always welcome and the door is open," Wais said.
"We... cannot imagine a political solution without the participation" of the absent factions, AU envoy Mohamed Lebatt said.