Chad said Monday it was suspending its efforts to mediate in the conflict in Darfur region until Sudan withdrew armed men massed along the border.
"Until these measures are taken, there is no question of Chad continuing its mediation" of the conflict in Darfur, said presidential communications director Abderaman Kulamalah.
Ismail said Ndjamena still had to formally inform Khartoum about its decision.
"We have not yet received an official notification from Chad that it has decided to suspend the mediation efforts, but we have heard this in the media," the foreign minister said.
Chad played an important role in getting the Sudanese government and the two main rebel groups in Darfur, the Sudan Liberation Movement (SLM) and the Justice and Equality Movement (JEM), last year to sign a truce.
It continued to help narrow differences between the warring parties despite repeated violations by them of the Ndjamena ceasefire agreement.
Ndjamena was also instrumental in getting the rebels to agree to attend African Union-sponsored peace negotiations with the government in Abuja, Nigeria.
The talks broke off in December after the rebels and government traded accusations of ceasefire violation, but both parties on Monday expressed readiness to return to the negotiating table.
Ismail said the Chad's decision to suspend its role in mediating an end to the conflict, which has left an estimated 300,000 people dead and displaced some 2.4 million, "will not hinder the Abuja forum."