UNITED NATIONS (AP) — Secretary-General Antonio Guterres warned Wednesday that hard-won gains toward lasting peace in Central African Republic are threatened by fighting in the country's southeast and heightened ethnic tensions.

The U.N. chief called on all parties to stop the violence and "take action to avoid a further deterioration of the fragile security situation in the country," U.N. deputy spokesman Farhan Haq said.

The secretary-general and the U.N. Security Council, in separate statements, condemned the killing of two U.N. peacekeepers from Morocco in the southeastern town of Bangassou on Tuesday. Another Moroccan peacekeeper was killed there Sunday.

Central African Republic has been wracked by violence between Muslims and Christians since 2013 when predominantly Muslim Seleka rebels overthrew the Christian president and seized power. Anti-Balaka militias, mostly Christians, fought back, resulting in thousands of deaths, the displacement of hundreds of thousands more, and the flight of many Muslims to the country's north and across the border into Chad and Cameroon.

Despite peaceful elections in early 2016, violence has continued. Hundreds of people have been killed and roughly 100,000 have been forced to flee their homes just in the past two months.

Sectarian violence has moved into the impoverished country's central and southeastern regions, prompting warnings of a national conflict roaring back to life. In Bangassou alone, more than 150 people have died in fighting between militias and U.N. peacekeepers.

Guterres said Sunday's incident brought the number of U.N. peacekeepers killed in Bangassou this year to nine. He urged Central African Republic authorities to investigate all the deaths and bring those responsible to justice, Haq said.

"If allowed to continue, the prevailing situation risks undermining the hard-won gains achieved towards lasting peace," Guterres' spokesman said.

The Security Council said the two Moroccan peacekeepers who lost their lives Tuesday were killed by suspected anti-Balaka elements. Another Moroccan peacekeeper was injured in the attack.

Council members condemned all attacks and provocations against U.N. peacekeepers. It urged the government to investigate and prosecute those responsible, stressing "that attacks against peacekeepers may constitute war crimes."

The council also expressed its readiness to impose sanctions on individuals and groups responsible for such attacks.

Council members called on all parties to cease violence immediately and urged concerted action by Central African Republic's government, regional countries and the international community "to avoid a further deterioration of the situation."