A Ukrainian police officer was killed on Friday as violence continued in the nation's east, authorities said, amid signs that Ukraine is losing control of parts of its border with Russia.
Two other officers were injured in the attack near the separatist stronghold of Slavyansk by pro-Russian rebels who launched a mortar attack on a checkpoint after taking up position in a church, deputy interior minister Serhiy Yarovy said.
As violence continued throughout the nation's vast and heavily industrialised east, the authorities seemed to be losing control of the frontier with Russia.
The border post at Severnyi, 70 kilometres (45 miles) from the city of Lugansk, was completely deserted on Friday.
Pro-Russian fighters of the self-proclaimed "People's Republic of Lugansk" had ordered the Ukrainian border guards to leave, a local resident said.
"They departed yesterday," he said.
Two border barriers had been lifted and anyone was able to cross.
The "People's Republic of Lugansk" claims to be in control of up to 200 kilometres (125 miles) of border. Ukrainian authorities admitted for the first time on Thursday that they had been forced to abandon some checkpoints.
- Porous border -
The porous border is likely to complicate efforts by Ukraine's government to re-impose its authority in the east.
The government in Kiev says truckloads of armed men and military equipment are attempting to cross every day to support the rebels.
Ukrainian forces have been carrying out military operations in the region since April 13. Some 200 people have died in the ensuing violence.
Kiev's appointee to run Donetsk, Sergei Taruta, admitted on Friday that the "anti-terrorist" operation had not achieved its objectives.
He said the Ukrainian military is now facing professional fighters who have arrived from Chechnya in the Russian Caucasus, and South Ossetia, a separatist pro-Russian republic in Georgia.
But Taruta cautioned against attempts to bring peace with a blunt military campaign.
"Every new death is a tragedy for Donbas and creates 10 new terrorists," he said, referring to the largely Russophone region where fighting is currently taking place.
The insurgents currently hold more than 200 hostages of various nationalities, Taruta said, adding that his administration is in negotiations to secure their release.
Two observer groups from the Organisation for Security and Cooperation in Europe -- eight people in total -- disappeared late last month and are thought to be being held in Lugansk, according to a pro-Russian rebel leader.
Russian President Vladimir Putin and Ukraine's president-elect Petro Poroshenko met on Friday for the first time since the crisis began during D-Day events in Normandy.
Putin's spokesman said both leaders are calling for an end to bloodshed and violence on both sides.