KIEV - Three Ukrainian servicemen were killed in fighting with pro-Russian rebels in the east of the country as fighting intensified in the region, Kiev said on Sunday.

Ukraine's defence ministry said one soldier was killed in fighting late on Saturday. The country's security service (SBU) later on Sunday confirmed two other servicemen were killed in shelling in the Luhansk region.

"In addition, four of our servicemen were injured in varying degrees of severity," Dmytro Gutsulyak, spokesman for the Ukrainian defence ministry, said.

The situation in eastern Ukraine has seen an uptick in violence in recent weeks. Two Ukrainian soldiers and four civilians - including a 13-year-old boy - were killed in fighting last week.

The chief monitor of the Organisation for Security and Co-operation in Europe (OSCE) special mission to Ukraine Alexander Hug temporarily left the conflict zone last week due to a "serious deterioration of the security situation", the organisation said.

More than 10,000 people have been killed since the Moscow-backed insurgency broke out in April 2014 following Russia's annexation of Crimea from Ukraine.

Ukraine and its Western allies accuse Russia of funnelling troops and arms across the border to fan the flames of the conflict.

Moscow has denied the allegations despite overwhelming evidence that it has been involved in the fighting and its explicit political support for the rebels.