Mr Nimeiri, who ruled the country for 16 years between 1969 and 1985, arrived in Khartoum with his family on board a flight from Egypt.

The BBC's Barbara Plett in Cairo: 'Nimeiri plans his political comeback'

He was welcomed by senior government officials, who had invited him to take part in celebrations marking the 30th anniversary of his coming to power. The current President, Omar al-Bashir, was not present at the airport.

Women ululated and men shouted "God is Great" as the 69-year-old former ruler stepped from his plane .

Supporters wave pictures of Mr Nimeiri after his coup

Mr Nimeiri is believed to be planning a political comback at the head of a newly-registered party, although diplomats in Khartoum say he has no solid popular power base.

Although he is due to visit for only two weeks, the government is reported to have offered Mr Nimeiri a permanent state residence.

Opposition groups have threatened to stage demonstrations and to take legal action against Mr Nimeiri.

The opposition Umma party said it would take him to court for committing "massacres" against followers of the Ansar religious sect in their strongholds in Sudan.

The Umma party's Sadiq al-Mahdi

The leader of the Umma party and the Ansar sect, Sadiq al-Mahdi, is himself in exile. Mr al-Mahdi became prime minister after General Nimeiri was ousted by popular protests in 1985.

But after only a short period of democratic civilian rule, the army under General Bashir seized power in 1989, backed by Islamist hard-liners.

In September 1983, President Nimeiri introduced Islamic Sharia law to Sudan; the legislation has remained in force ever since.