Aljazeera reported that the coup was scheduled for 1100 GMT shortly after Friday prayers.
Troops patrolled the streets in downtown Khartoum during the day. They closed off areas surrounding President Umar al-Bashir's residence, army headquarters and other government buildings and searched cars at checkpoints.
Sudanese authorities said they had captured all involved in the alleged coup plot.
On 8 September, 70 Popular Congress members were arrested in Khartoum with three large caches of rifles, mortars and other weapons allegedly found in their possession. The government claimed the cache was to be used in a plot to sabotage the country.
Once a member of the currently suspended Popular Congress led by Hasan al-Turabi, Muhammad al-Hasan al-Amin on Friday alleged that some party members were making "military preparations" in the face of a government crackdown.
Al-Amin's allegations came a week after he resigned from the Popular Congress.
"The main reason I defected is that some members of the party were doing what I call military preparations," he said.
But the Popular Congress denied the charge, saying al-Amin's allegations were made under duress.
Al-Amin said the military preparations might have been done "with the consent of some of the leaders".
"This activity is contrary to my beliefs. As a Muslim, it is forbidden to use military methods to take power," he said.
The deputy leader of the Popular Congress, Abd Allah Ahmad said al-Amin had defected under pressure from the authorities and denied the party had planned armed action.
Al-Amin declined to say who in the party was taking up arms. He said he had been arrested and interrogated for six days before agreeing to release the information that the party was planning military action.
The Sudanese president, in comments to the Sudanese Media Centre, said the plot had been to sabotage the nation by targeting the centre of Khartoum.
The government has threatened to take legal action against the Popular Congress, which could lead to its banning.
The party has been suspended since April for inciting tribal tensions in the troubled region of Darfur.
The Popular Congress has accused the authorities of torturing detained party members and said one man died in detention.
The government has said it is investigating the case.