Sudanese paramilitary forces are pushing deeper into Khartoum, witnesses say, after a crackdown on protesters killed at least 30 people on Monday.
Heavily armed members of the Rapid Support Forces are said to be fanning out across the capital and the neighbouring city of Omdurman, clearing barricades and firing into the air.
The military has faced international condemnation for the deadly crackdown.
It has ended a pact with the protesters over a transition to civilian rule.
The two sides had initially agreed a three-year transition, culminating in elections. On Monday, however, the Transitional Military Council (TMC) said polls would be held within nine months.
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The demonstrators had argued that a longer period was needed in order to guarantee fair elections and dismantle the political network associated with the former government of President Omar al-Bashir.
After 30 years in power, Mr Bashir was overthrown by the military in April, amid pressure from the protesters.