Sudanese President Omar Hassan al-Bashir has pardoned nine army officers, days after they were jailed for their role in an alleged coup attempt, state news agency SUNA reported.

The brief report issued on Wednesday did not say why Bashir had ordered their release - and the pardon did not include other senior officials the government said were caught up in the plot, including the country's former head of intelligence.

The army officers had been sentenced on April 7 to prison terms of between two and five years. The trial of former spy chief Salah Gosh and other security officers has yet to start.

Bashir had ordered the release of all political prisoners at the beginning of the month as part of a general amnesty. It was not immediately clear if Wednesday's releases were part of that programme.

Hundreds of supporters of one of the released men - Wad Ibrahim, a senior army officer - gathered outside his Khartoum home to celebrate.

Ibrahim told the Reuters news agency at his house he had only been interested in pushing for reform. "We thank the Sudanese people and the armed forces ...(I hope) the country will reform and people will unite," he said.

President Bashir was a senior army officer when he came to power in his own coup in 1989 and built his power base on an alliance between Islamists and the country's powerful military.

During his near 24-year rule, he has weathered rebellions, US trade sanctions, the loss of most of the country's oil with the secession of the country's south in 2011 and an arrest warrant from the International Criminal Court over his crackdown on a revolt in the western region of Darfur.

High food prices in Sudan caused by the loss of the oil - and with it the source of foreign currency used to import wheat and other staples - have triggered some protests against Bashir since the South seceded in July 2011.

Some members of the army and the ruling National Congress Party have also complained that Bashir and other senior leaders have abandoned the Muslim values of the 1989 bloodless coup that brought him to power.