The United Nations says the number of people killed in a year of fighting in Ukraine has now passed 6,100, and says it's increasingly worried that breaches in a cease-fire will further worsen the human rights situation in parts of the country's east.

The U.N. human rights office in Geneva estimated Friday that at least 6,116 people have been killed and 15,474 wounded since last April. It said the actual number of casualties could be significantly higher.

The office said at the beginning of March that the number of dead had topped 6,000.

It said Friday that about 400 civilians have been killed since the beginning of this year, in both government and rebel-held areas, either in indiscriminate shelling of residential areas or by land mines and unexploded ordnance.