Sudan foiled a plot by Islamists to overthrow the government on Friday afternoon, the Interior Ministry said in a statement.

Elements of the Popular Congress (PC) headed by jailed Islamist leader Hassan al-Turabi planned to carry out the plot in Khartoum at 2 p.m. (1100 GMT) right after the Friday prayers, said the statement.

Nearly all those involved in the coup attempt have been arrested except the alleged ringleader Al-Haj Adam Youssef, a communications official of the opposition party, it said.

The ministry further called on the people to offer information on Youssef's whereabouts.

It warned that "harboring him or withholding information that would lead to his arrest would be a crime punishable by law."

Sudanese President Omar el-Bashir said shortly after the crackdown that the opposition's plot had been to sabotage the nation by targeting the center of the capital.

Security was beefed up in downtown Khartoum on Friday, with areas surrounding the presidential residence, the army headquarters and other government buildings cordoned off by government forces.

The authorities arrested dozens of PC members in Khartoum this month after discovering three large caches of ammunition they said were to be used in a coup plot.

The PC has been suspended in the country since April, when it was accused of inciting tribal tensions in the troubled western region of Darfur.

Its leader Turabi, a former mentor of Bashir, was arrested at that time and is facing charges such as incitement to sedition and subversion of the current regime.