More than 600 people have been killed and 159,000 displaced in sectarian violence between Christians and Muslims that has ravaged the Central African Republic in the past week, according to the UN's refugee agency.

450 people had been killed in the capital Bangui and 160 others were killed elsewhere in the country over the past week, the UNHCR said on Friday.

"We are seeing a further deterioration in the situation in Central African Republic," UNHCR spokesman Adrian Edwards said.

Reporting from Bangui, Al Jazeera's Nazanine Moshiri said that attacks were still happening around the country.

The latest attack took place by the anti-Balaka militia on the village of Bohang, in the west of the country. At least 27 people were killed in that attack, which targeted Muslims, she reported.

Aid workers say a humanitarian crisis is looming in CAR, as over 500,000 people have been displaced from their homes across the country since the fighting began, according to the Reuters news agency. Tens of thousands have also sought refuge in makeshift camps surrounding the capital.

"We have noticed several cases of traumatized people, a few cases of survivors of gender-based violence, and also a few cases of separated children [from] their families," UNHCR's Maurice Azonnankpo told Al Jazeera from CAR.

"We have our teams at all the [internally-displaced persons] sites where they are conducting distribution of non-food items... to respond to the needs of these IDPs in Bangui."

Troops to increase

The UN secretary-general made a personal appeal to those in CAR to stop the "bloodshed" there.

Ban Ki-moon's statement released on Friday calls on Christian and Muslim community leaders to act as "messengers for peace".

"The world is watching," the statement read. "You will be held to account." He also said that more French and African troops would come soon to "restore order".

Also on Friday, a senior African Union official told Reuters that the AU had authorised an increase in the force deployed to CAR from 2,500 to 6,000 troops.

"The decision by the Peace and Security Council (PSC) is to authorise us to increase the force. We can go up to 6,000, depending on the needs," El Ghassim Wane, the director of the AU's Peace and Security department, said.

"Within three months the PSC will meet again to review the strength based on the evolution of the situation and our assessment of the situation on what needs to be done," he said.

France also recently deployed more than 1,600 troops in the country to act with AU forces. The troops on the ground are trying to disarm militias awash in automatic weapons in cities and towns.

The fighting in the former French colony is between the mainly Muslim Seleka fighters - originally from neighbouring Chad and Sudan - and the Christian anti-Balaka, whose name means "anti-machete", the weapon of choice for Seleka.

The Christian fighters oppose the Muslim ex-rebels in charge of the CAR since March.

Michel Djotodia, rebel leader-turned interim president, has largely lost control of his loose band of fighters, who ended up being disbanded.

For the latest news from Central African Republic, follow Al Jazeera's Tristan Redman and Nazanine Moshiri, who are on the ground in CAR, on Twitter.

Source: Al Jazeera and agencies