It now seems inevitable Sudan will be confirmed as one of the world's pariah states. The Khartoum government is accused of harbouring internationally wanted terrorists and of having abetted an attempt on the life of the Egyptian head of state.
A UN Security Council resolution, calling on Sudan to surrender three terrorist suspects and desist from terrorist activities, expires at the end of the month. If Khartoum fails to comply, Western diplomats say, it will face another resolution, this time imposing sanctions.
Khartoum denies harbouring three Egyptians wanted in connection with the attempted assassination last year of the Egyptian President, Hosni Mubarak. This week Lieutenant General Omar al-Bashir, Sudan's military leader, told Salim Ahmed Salim, the visiting Organization of African Unity secretary-general, that the three men were not in Sudan.
But there is damning evidence that the ruling National Islamic Front (NIF) and the state security service were involved in the attack in the Ethiopian capital, Addis Ababa, last June.
"Though the Sudanese probably didn't order the attack, we have no doubt that they facilitated travel documents for the terrorists, provided them with cover in Khartoum and transported their weapons", says an Ethiopian official who participated in drafting his government's submission to the Security Council. "The terrorists received the blessing, active support and encouragement of the NIF".
Eleven Egyptians were deployed to carry out the attack by the extremist group, Jamaat Islami, which seeks to overthrow President Mubarak and install a strict Islamic regime in Egypt.
Five were killed at the time of, or shortly after, the assassination attempt. Three were arrested in Ethiopia and are now in custody. Three escaped.
Ethiopia, Egypt and the United States, which has placed Sudan on a shortlist of states sponsoring terrorism, believe the three escapees are in Sudan. They have been named as Mustafa Hamza, Izat Yassin and Husayn Ahmed Shahit Ali, also known as Siraj Mohamed Hussein.
Sudan admits Siraj flew to Khartoum on a Sudan Airways flight after the attack but insists he is no longer in the country. Knowledge of the other two suspects is denied, as is involvement in the preparation of the attack.
Khartoum has issued arrest warrants for the three and has sent envoys on an global round of damage limitation. But the international community is not convinced. Diplomats interviewed by the Independent in Sudan and in neighbouring countries say that the evidence against Khartoum is incontrovertible.
The three Egyptians in custody confirm that they were harboured by Sudan after their arrival from Pakistan, where they had been based as mujahedin - fighters in the Islamic cause. They have given precise details of where they were housed in Khartoum while they planned the attack. The group carried Sudanese or Yemeni passports, which were prepared for them in the Sudanese capital.
The weapons used in the ambush near Addis Ababa airport were flown to the capital of Ethiopia from Khartoum by Sudan Airways. After the attack, a box dispatched by Sudan's General Security Bureau was found in a "safe house" used by the terrorists.
"The Sudanese government might not have been involved in planning the attack but we're sure that it gave Jamaat the facilities it needed", an Egyptian diplomat said. "There are also strong indications their security services were involved".
Diplomats believe President Bashirto had no advance knowledge of the attack and say he was angered when he heard of it. His dismissal of Dr Nafie Ali Nafie, head of the Sudanese External Security Service, is seen as confirmation the organisation was involved in the plot.
It is not thought possible that the terrorists could have prepared their mission without the assistance of the NIF which, under the leadership of Dr Hassan al-Turabi, exists alongside the country's formal system of government. The NIF is committed to the export of Islamic fundamentalism to neighbouring countries.
"People of a variety of nationalities are being trained in terrorist activities in Sudan", a Western diplomat says. "The government and the NIF are perfectly capable of acting against any of these terrorist entities should they wish".
The US, which last month withdrew its embassy staff from Khartoum because of "security risks" and in protest against Sudan's alleged links with terrorism, says there are up to 20 training camps for Muslim militants inside Sudan.