The violence erupted on Monday between rival factions of the so-called former Seleka Muslim rebel group in the town of Bria, 400 kilometres (250 miles) northeast of Bangui, MINUSCA said in a statement.
"The MINUSCA base was targeted by some elements of the FPRC before they were driven out of the area by retaliatory fire," it said.
The FPRC -- the Popular Front for the Renaissance of the Central African Republic -- is a splinter group led by Noureddine Adam, who faces international sanctions for his alleged role in intercommunal killings in 2013 and 2014.
The other ex-Seleka faction involved in Monday's fighting was the Union for Peace in Central Africa (UPC), MINUSCA said. The group is led by Ali Ndarass.
The statement said the two groups would be "held responsible for the violence, particularly on civilians." It gave no details about any casualties.
One of the world's poorest countries, CAR has been struggling to emerge from the aftermath of a civil war which erupted in 2013 following the overthrow of former president Francois Bozize, a Christian, by Muslim rebels from the Seleka coalition.
Militias are flourishing, given the weakness of the state. The main groups are factions from the former Seleka and Christian "anti-Balaka" (anti-machete) militias, a reference to the rebels who use machetes.
France, the former colonial power, last month withdrew a military mission it deployed in December 2013 to stabilise the country, leaving the UN's 12,500-strong MINUSCA peacekeeping mission to protect civilians from armed groups.