Northern Ireland police fired six baton rounds and nine officers were injured during a second night of rioting in north Belfast, police said.
Three officers were hospitalised after suffering injuries in the unrest, which first erupted on Sunday when loyalists from the Protestant community attempted to disrupt a march by Catholic republicans.
On both nights, loyalists and republicans gathered in the Carlisle Circus area and pelted police with petrol bombs, bricks, stones and fireworks as they tried to keep the two groups apart.
A van was also hijacked on Monday and pushed into police lines prompting police to deploy four water cannons.
The chairman of the Northern Ireland Police Federation, Terry Spence, praised the "bravery and courage" of the frontline officers, saying it was "in stark contrast to that of the cowardly thugs responsible for trying to murder them".
Four officers received hospital treatment following Sunday's disorder while 43 others were treated for various minor injuries.
"I am both angry and sad that my officers have been subjected to such significant attack," said Northern Irish police chief superintendent George Clarke.
Around 3,500 people died in the three decades of sectarian violence between Northern Ireland's Catholics and Protestants that largely ended with a 1998 peace agreement, though sporadic unrest and bomb threats continue.