Sudanese security forces have detained nearly two dozen opposition leaders, who were on their way to deliver a petition to the presidential palace calling for President Omar al-Bashir to resign.
Media reports said opposition leaders belonging to several political parties were arrested while gathering in downtown Khartoum on Thursday.
The arrests took place as they were getting ready to deliver the petition, which demanded the formation of a new transitional government to replace Bashir and his administration.
In a statement, the Sudanese Congress Party confirmed that authorities "pre-empted" demonstrations. It said deputy head of Umma Party Mariam Sadiq al-Mahdi, the party's secretary general Sara Naqdallah and Communist Party leader Mokhtar al-Khatib were arrested.
The spokesman of the Sudanese Professionals’ Association (SPA), the main protest organizer, was also arrested.
Later, police fired tear gas to disperse hundreds of angry protesters who had gathered to march near the Arab Market area in the capital city.
Protesters held anti-government placards and chanted slogans such as "Peaceful, peaceful against the thieves" and "Fall, that's it" to send the message that their only demand was Bashir's fall.
The detentions amount to the largest crackdown against the opposition in one day since the demonstrations began two months ago.
Official figures show 30 people, including some security agents, have lost their lives since the onset of the rallies. Activists and some rights groups say nearly 60 people have died so far.
Since December, Sudan has been rocked by a wave of protests calling on Bashir, who seized power in a 1989 military coup, to step down.
The country’s security forces have so far used tear gas, stun grenades and live ammunition to break up demonstrations, and detained hundreds of protesters and opposition figures.
The president has remained defiant, addressing loyalists at a number of rallies across the country and seeking support from regional allies.
Bashir and other senior Sudanese officials have repeatedly said that the government can only be changed through elections. The 75-year-old veteran leader is considering running for a third presidential term in next year's elections.
Sudan has been struggling with a worsening economic crisis, including a serious shortage of foreign currency. The cost of some commodities, including medicine, has more than doubled and inflation has hit 70 percent. A growing lack of food and fuel has also been regularly reported across several cities, including Khartoum.
Bashir is wanted by the International Criminal Court over charges of masterminding genocide in the Darfur region.
President Bashir, who has cultivated close ties with Saudi Arabia, has also stressed his intention to continue participating in the war on Yemen.