* Ukraine says six soldiers killed in past day
* Local officials say four civilians killed in air strike
* Kiev appears to blame Russia for air attack
* Diplomats push for ceasefire talks
By Natalia Zinets
KIEV, July 15 (Reuters) - At least six Ukrainian soldiers were killed in renewed attacks on government military posts and checkpoints by pro-Moscow separatists near the border with Russia, the Ukrainian military said on Tuesday.
There were also reports of an air strike killing four civilians in the small town of Snizhne, for which Kiev denied responsibility and appeared to point a finger at Russia - two days after Moscow threatened retaliation for the death of man when a shell landed on the Russian side of the border.
"Today at 7 a.m. (0400 GMT) an unknown plane carried out a bombing attack on Snizhne. The flight can be described only as a cynical provocation," Andriy Lysenko, a spokesman for Ukraine's National Defence and Security Council, told reporters.
His remarks appeared to be an accusation against Russia, since the rebels have not used aircraft in the conflict.
Fighting over the past four months between forces of the pro-Western Kiev government and separatists who want union with Moscow has intensified since last Friday, with Ukraine and Russia blaming each other for cross-border attacks and little prospect of a ceasefire.
Vladyslav Seleznyov, spokesman for Kiev's "anti-terrorist operation" in the east, said rebel fighters had attacked military posts in several different areas overnight.
"As a result of a Grad missile attack during the night, two Ukrainian soldiers received fatal wounds," he told Fifth Channel television.
Security council spokesman Lysenko said six Ukrainian soldiers in all had died in the past day and 13 were wounded.
Municipal officials said at least four civilians had been killed in Snizhne, 20 km (12 miles) from the border with Russia, in what separatist rebels said had been an air strike by a Ukrainian warplane.
A separatist spokesman, quoted by Russia's Interfax news agency, said 10 people had been killed.
Government officials, however, that flights by Ukrainian warplanes had been suspended since Monday when a Ukrainian Antonov An-26 transport plane, carrying eight people, was downed in a rocket attack which Kiev said may have come from Russian territory.
Lysenko said two of the crew who survived appeared to have been taken captive.
Ukraine has said there is now clear evidence of direct Russian involvement in the fighting which intensified over the weekend with Ukrainian air strikes on rebel positions.
Well over 200 Ukrainian servicemen have been killed as well as hundreds of civilians and rebels since violence erupted in Ukraine's Russian-speaking east following a pro-Europe revolt in Kiev that ousted a Moscow-backed president in February and led to Russia's annexation of Crimea.
Ukrainian President Petro Poroshenko, pressing the European Union to take a harder line with Moscow possibly involving new tougher sanctions, said on Monday that Russian military officers were now fighting alongside separatists and heavy military equipment is pouring across the border from Russia.
Poroshenko, elected in late May, refused on June 30 to extend a 10-day unilateral ceasefire which he said had been breached repeatedly by the separatists. He renewed the government's military campaign to break rebel resistance.
The separatists, who have set up 'people's republics', have been pushed back into the main eastern city of Donetsk, though they remain also in control of the border city of Luhansk.
German Foreign Minister Frank-Walter Steinmeier, in a new peace effort, said a diplomatic contact group might talk to separatists by video conference on Tuesday and meet them in person soon afterwards.
He said all parties were making a "strong effort" for the group - which includes Russia, Ukraine and the Organization for Security and Cooperation in Europe - to hold the video conference and agree a venue for a direct meeting with the rebels.
Moscow has invited foreign military attaches to visit the Russian town hit by fatal shelling on Sunday, an event for which it threatened "irreversible consequences". Ukraine denied that its armed forces were responsible for the incident. (Additional reporting by Lidia Kelly in Moscow; Writing by Richard Balmforth; Editing by Alastair Macdonald)