Invitations had been issued to heads of IGAD member-sates to a summit proposed for a date around 20 August, the official said.

IGAD mediated the peace process that culminated in the 9 January Comprehensive Peace Agreement signed by Garang and Sudan’s President Umar el-Bashir in Kenya, ending over two decades of civil war that killed close to two million people.

"We have sent out invitations and are awaiting confirmation. We have proposed 20 August as the summit day, but this may change depending on the response from heads of state from the region," a senior foreign ministry official told IRIN.

"We want to evaluate the situation following Garang's death and give a reassurance that the region is committed to the Sudan peace process," the official, who declined to be named, said.

Amid ongoing tension in Khartoum following violence that claimed dozens of lives after news of Garang’s death in a weekend helicopter crash, fear abounds that Sudan's fragile peace process is under threat.

In a related development, Uganda, in whose helicopter Garang perished, has announced a national mourning ceremony on Thursday at the country's independence square in the capital, Kampala, for victims of Saturday's air crash, including Garang.

The Ugandan foreign minister in charge of international affairs, Okello Oryem, told reporters that Thursday had been declared a national holiday in honour of Garang - a long-time friend of President Yoweri Museveni.

The bodies of the Ugandans who died during the crash were flown home on Wednesday and would lie at Kololo Independence Square during the national ceremony. The government said it would meet the burial expenses for its nationals who died in the accident.

Oryem said Uganda would be represented at the funeral of John Garang in Juba on Saturday, by "a high powered delegation headed by the highest authority in the country," refusing to confirm whether the "highest authority" would be President Museveni himself.

Oryem said a team of three aviation experts would join the main team of investigators from the Sudanese government to probe the accident that involved a Ugandan presidential helicopter, though the Ugandan government has maintained that it was an accident caused by bad weather.