On Saturday, embassy and United Nations vehicles were targeted by demonstrators.
The head of the UN's MONUSCO peace-keeping mission Bintou Keita said on X, formerly Twitter, that several of its vehicles had been set alight.
Protests broke out last week in the capital Kinshasa and the southeastern city of Lubumbashi.
On Friday, dozens of youths demonstrated outside the embassies of France and Britain, and earlier in the week, in front of the U.S. embassy.
"The government has decided to strengthen the security arrangements in different embassies as well as in the premises of MONUSCO," it said late Sunday in a statement after an urgent meeting.
It added that an inquiry had been opened and the government "strongly condemns these totally unjustified acts of violence."
AFP journalists early on Monday saw that policing had been increased at several sites in the capital.
Dozens of youths were also gathering for new marches and had burnt tires on the pavement.
As a precaution, foreign schools were closed on Monday morning, as well as some shops in the center of Kinshasa.
"It's them who are killing in DRC. Westerners in general must leave our soil," a demonstrator named Gedeon, who was near the US embassy, said to AFP.
A placard he was carrying read in English and French: "Paul Kagame (the Rwandan president) friend to the Westerners who kill in the east of the DRC."
Tires were also burned near MONUSCO headquarters by protesters who were dispersed by security forces.
The M23 has seized vast swathes of North Kivu since emerging from dormancy in late 2021, in an area wracked by violence for decades following regional wars in the 1990s.
The DRC, the United Nations and Western countries say Rwanda is supporting the rebels, an allegation Kigali denies.
Clashes have intensified recently around the city of Goma, the capital of North Kivu province, forcing thousands of people to flee.
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