Chad has closed its border with Sudan, in response to Khartoum's decision to break diplomatic relations with N'Djamena following a rebel attack on the Sudanese capital.
The Chadian government issued a statement Monday saying it had sealed the border and frozen economic ties with Sudan, to avoid all infiltration and suspicious traffic.
Chad denies any involvement in Saturday's unprecedented attack by Darfur-based rebels on Khartoum and its twin city, Omdurman.
But the Sudanese government holds Chad responsible for the assault by the Justice and Equality Movement.
Sudanese forces are hunting for any rebels who remain in the capital area, after the army reported Sunday killing 46 fighters and capturing 300 others.
The government has restored a curfew in Omdurman, and witnesses say many soldiers are deployed throughout the city. Gunfire has been reported in Omdurman and Khartoum.
Rebel leader Khalil Ibrahim told reporters by phone Monday that he is still in Omdurman, and he promised more attacks on the government.
Sudanese authorities have released opposition leader Hassan al-Turabi after about 12 hours in detention. Security forces arrested Turabi earlier Monday for suspected links to Ibrahim and the Justice and Equality Movement.
At least four members of Turabi's Popular Congress party also were arrested. Opposition party members are denying they support or have influence over the rebels.
Chad and Sudan regularly accuse each other of supporting rebel movements in each country. In February, Chad accused Sudan of supporting an attack on the Chadian capital, N'djamena, by Chadian rebels.
The Justice and Equality Movement is considered the strongest of the many rebel groups operating in Sudan's troubled Darfur region.
Fighting between the rebels, the government and government-backed militia has dragged on for more than five years. U.N. officials estimate that more than 200,000 people have died in the conflict, and that more than 2.5 million have been made homeless.
Some information for this report was provided by AFP and Reuters.