* Councillor mobbed before he disappeared
* Killings prompt EU call for Russian restraint
* Ukraine security service names two suspects (Adds security service statement)
SLAVIANSK, Ukraine, April 23 (Reuters) - The Ukrainian town councillor whose apparent torture and murder helped to prompt a threatened new government offensive in the east was mobbed by a hostile, pro-Russian crowd before he disappeared, a video of the incident shows.
The apparent murder of Volodymyr Rybak and a second man prompted the European Union to call on Russia to use its influence to stop kidnappings and killings in mainly Russian-speaking eastern Ukraine, scene of separatist rebellions against Kiev's leaders.
Ukraine's security service said a rogue officer and a member of Russian military intelligence were involved in Rybak's killing.
The footage from April 17 on local news site gorlovka.ua shows angry scenes outside the town hall of Horlivka, between the separatist flashpoint cities of Donetsk and Slaviansk, as Rybak is manhandled by several men, among them a masked man in camouflage, while other people hurl abuse.
Rybak had tried to remove the flag of the separatist Donetsk Republic, the website said. "Over my dead body will you take down that flag," one man in plain clothes yells at Rybak as the politician tries to gain entry to the town hall.
Two uniformed policemen appear in the video, though only one appears to intervene - ineffectually. After several minutes, Rybak appears able to walk away. Ukraine's interior ministry said he was seen being bundled into a car by masked men in camouflage later that day. His body was found on Saturday near Slaviansk.
He and another, unidentified, man appeared to have been tortured and dumped alive in a river to drown, police concluded.
Ukraine's acting president, who like Rybak is a member of the Batkivshchyna party led by former premier Yulia Tymoshenko, cited the murder as grounds for relaunching a so far limited operation against militants who have taken over around a dozen towns and public buildings in the Russian-speaking east.
"Terrorists who have effectively taken the whole Donetsk region hostage, have crossed a line, starting to torture and murder Ukrainian patriots," Oleksander Turchinov said on Tuesday night.
Kiev authorities acknowledged on Wednesday that a limited "anti-terrorist" operation had not yet resumed. But First Deputy Prime Minister Vitaly Yarema said: "In the near future, appropriate measures will be taken and you will see results."
In Brussels, a spokesman for EU foreign policy chief Catherine Ashton pressed for all parties who attended four-way talks in Geneva last week to implement an accord that calls for moves to demilitarise the region and for occupied buildings to be vacated.
"We call ... in particular on Russia to use its leverage to ensure an immediate end to kidnappings and killings in eastern Ukraine," the spokesman said.
In Slaviansk near where Rybak's body was found, the town's self-declared separatist mayor, Vyacheslav Ponomaryov, blamed Ukraine's Right Sector nationalist group for the murder.
"This is all being done by the Right Sector. They are constantly trying to discredit us," Ponomaryov said. "I went to the morgue to see both corpses, they had traces of torture on their bodies and hands."
Ukraine's SBU state security service issued a statement accusing a rogue SBU officer and an officer in Russia's GRU military intelligence of involvement in Rybak's murder.
Without elaborating the source of its information, the SBU said GRU Lieutenant-Colonel Igor Bezler ordered pro-Russian militia in Horlivka to "neutralise" the town councillor.
It said Igor Strelkov, whom it has previously accused of being a GRU agent formerly working inside the SBU, had ordered Rybak taken to the headquarters of the separatists in Slaviansk. (Reporting by Alastair Macdonald and Sergei Karazy in Kiev and Aleksandar Vasovic in Slaviansk; Writing by Alastair Macdonald and Richard Balmforth; Editing by Giles Elgood)