The interim Ukrainian president reinstated military conscription Thursday in the face of an increasingly empowered pro-Russian separatist insurgency in the country\’s eastern regions.
The move comes a day after Turchynov said that his government was "helpless" to quell the growing pro-Russian separatist movement in two eastern regions and could not control its own troops.
Turchynov also said Ukraine was on "full combat alert", amid fears Russian troops could invade.
"I would like to say frankly that at the moment the security structures are unable to swiftly take the situation in the Donetsk and Luhansk regions back under control," he said during a meeting with regional governors.
He admitted security personnel "tasked with the protection of citizens" were "helpless".
"More than that, some of these units either aid or co-operate with terrorist groups," he said.
Turchynov added: "Our task is to stop the spread of the terrorist threat first of all in the Kharkiv and Odessa regions."
The acting president said that the tens of thousands of Russian troops stationed just over the border meant that "the threat of Russia starting a war against mainland Ukraine is real".
In Donetsk on Thursday, pro-Russian militants attacked the prosecutor\’s office, accusing those inside of siding with the government in Kiev.
The crowd later forced its way into the building, stripping weapons and shields from police officers and raising the flag of the self-proclaimed Donetsk People\’s Republic.
Many attackers chanted "Fascists! Fascists!". There were reports of injuries on both sides.
One policeman running away from the prosecutor\’s office told the BBC\’s Steve Rosenberg: "How on earth can we deal with this kind of thing?"
Donetsk, an industrial hub of more than one million people, has seen a number of government offices seized in recent weeks.
Activists have seized scores of government buildings and taken hostages including international monitors.
Oleksandr Turchynov\’s admission came Wednesday at a meeting with regional governors in Kyiv. He singled out mounting difficulties in the Donetsk and Luhansk regions, where he said some military units are "cooperating with terrorist organizations."
The mayor of Kharkiv, who has been credited with maintaining calm in Ukraine\’s second city, was shot in the back earlier this week while cycling, as separatists tighten their grip on large parts of the east.
Hours before Turchynov spoke, local authorities in the east said gunmen had seized control of a city council building in Horlivka, a city of 290,000 residents north of the industrial hub of Donetsk. Separatists now control about a dozen cities in Ukraine\’s industrial east, including Donetsk, where rebels have set a referendum on secession for May 11.
A similar vote last month led to Russia\’s annexation of the Crimean peninsula.
Meanwhile, negotiations continue for the release of seven European observers taken hostage last week in the eastern city of Slovyansk.
The self-proclaimed pro-Russian mayor of that city said Tuesday he would be willing to swap the observers for pro-Russian activists held by Ukrainian authorities. On Wednesday, he told reporters the talks are hindered by "technical" matters. He did not elaborate.
In Washington Wednesday, the top Republican on the Senate Foreign Relations Committee, Bob Corker, called for deeper sanctions targeting Russia\’s energy and banking sectors. He said current sanctions aimed at forcing Moscow to ease tensions in Ukraine are not adequate.
The US and EU have accused Russia of failing to implement the terms of a deal agreed in Geneva aimed at defusing the crisis by disarming illegal militias. Moscow blames Kiev for the unrest and has condemned the sanctions.
Russia, which annexed the Crimea region from Ukraine last month, has said it has no plans to invade the east.
President Vladimir Putin has insisted there are "neither Russian instructors, nor special units nor troops" inside Ukraine.
However, Moscow has also warned that its soldiers are ready to act if Russian interests are threatened.
Some 40,000 Russian troops are stationed near the Ukrainian border.