Keiv -- Ukraine scrambled jet fighters to strike at rebel positions early on Saturday, after separatists resumed missile attacks on government forces near the frontier with Russia, the border guard service said.

In a night of violence in several areas of eastern Ukraine following a missile strike by separatists on Friday that killed at least 23 government servicemen, Ukrainian forces also used artillery to respond to rebel fire, the military said.

Ukrainian President Petro Poroshenko had pledged to "find and destroy" the pro-Russian rebels responsible for the missile attack at Zelenopillya, which also wounded nearly 100.

At least two more Ukrainian soldiers were killed and about 20 injured on Saturday in a mortar and missile bombardment by the rebels of army checkpoints at Dyakove and Nyzhnoderevechka near Luhansk, the government's "anti-terrorist" operation said.

Luhansk, like the main industrial city of Donetsk, is controlled by pro-Russian separatists who set up 'people's republics' in Russian-speaking areas and declared a wish to join Russia in response to a pro-Western revolt in the capital Kiev.

Rebel fighters meanwhile said that Ukrainian fighter planes had carried out air strikes on Saturday in the eastern town of Horlivka.

"There were a series of powerful explosions. Details are being clarified," a separatist representative, Konstantin Knyrik, was quoted as saying by Russia's Interfax news agency.

The Grad missile strike on Friday on a motorised brigade at Zelenopillya was one of the deadliest against government forces in three months of fighting since the separatist rebellions erupted following Russia's annexation of Crimea.

Poroshenko, whose forces had recently seemed to be prevailing over the rebels, said they would pay for the strike in their "scores and hundreds".

The border guard service in a statement said army and border guard units had again come under missile attack in several areas near the border just after midnight.

"The Ukrainian armed forces returned artillery fire. On the defence minister's order, fighter jets went up to patrol Ukraine's air space and be ready to deflect further possible attacks," it said.


Friday's military setback at Zelenopillya took the gloss off the government's recapture of the rebel stronghold of Slaviansk last weekend, and seemed likely to add a new sense of urgency to diplomatic attempts to end the worst crisis between Russia and the West since the Cold War.

The Ukrainian military, following the Slaviansk victory, says it has readied a plan to oust the rebels now from Donetsk, a city of 900,000 people where separatist forces are dug in.

Poroshenko has said the military plan will be aimed at protecting civilians there and has appeared to rule out the use of air strikes and artillery to crush the rebels.

Poroshenko, who was also urged by German Chancellor Angela Merkel to use a sense of proportion in actions against separatists, had further talks on Friday with Donetsk mayor Aleksander Lukyanchenko on the issue.

Western allies and Russia are pressing for a new meeting of the 'contact group' involving separatist leaders to try to negotiate an end to the crisis.

Poroshenko says he has proposed various venues for these talks to take place but has said there will be no repeat of a 10-day unilateral ceasefire by government forces which lapsed on June 30.

The Ukrainian government says that ceasefire was repeatedly violated by the rebels and that more than 20 Ukrainian servicemen were killed while it was in force.