By Pavel Polityuk and Natalia Zinets
KIEV (Reuters) - Pro-Ukrainian activists prevented repairs to sabotaged power lines leading to Crimea on Monday, keeping the Russian-annexed peninsula starved of electricity for a second day and tensions between Moscow and Kiev high.
Ethnic Tatars and members of Ukrainian nationalist battalions largely blocked access for engineers to four pylons in Kherson, a region of the Ukrainian mainland controlled by Kiev, which unknown attackers blew up over the weekend
"Teams are ready to fix the consequences of the blasts in the course of four days," said Igor Boska, the regional head of state power supplier Ukrenergo.
"When this can happen depends on the results of talks, which the instigators of the blockade are carrying out with authorities," he said in a statement posted on the Kherson administration's website.
Engineers began laying undersea cables from southern Russia to Crimea earlier this year to allow the contested territory, which is home to around 2 million people, to draw all its power from Russia by 2020.
But for now, the peninsula which Russia seized last year depends on Ukraine for at least 70 percent of its electricity and the first phase of the Russian project, which will ease dependence on Ukraine, is not due to come online until next month.
The annexation plunged relations between Kiev and Moscow into a crisis deepened by a rebellion by pro-Russian separatists in eastern Ukraine.
One Russian senator described the blasts as an "act of terrorism". But Mustafa Dzhemilev, a senior Crimean Tatar politician, said talks to restore power to Crimea could start only after "political prisoners" on the peninsula were released, according to an interview he gave to Ukrainian news agency Liga.
The annexation was opposed by many Tatars, a Turkic-speaking Muslim community with a long history in Crimea, and they have since held numerous protests to complain of discrimination and intimidation which they say is meant to silence dissent.
The peninsula's pro-Kremlin leadership denies a crackdown is underway.
In September, Tatar activists on the mainland set up road blocks on the two main routes leading into Crimea at the start of what they said was an economic blockade aimed at dramatizing the plight of their Tatar brethren living on the peninsula.
The activists deny they blew up the pylons, which also triggered blackouts in parts of Ukraine's Kherson. While preventing any work that would help restore electricity to Crimea, they said they would allow repairs to lines supplying mainland Ukraine.
Dmitry Peskov, a Kremlin spokesman, said Russia hoped Kiev would take "vigorous steps" to restore Crimea's power supplies.
Russia's Energy Ministry said emergency electricity supplies had been turned on for critical needs in Crimea and that mobile gas turbine generators were being used. Sergei Aksyonov, the Kremlin-backed head of Crimea, declared Monday a non-working day because of the emergency situation.
Russia's annexation of Crimea triggered punitive Western sanctions on Moscow, which a diplomat told Reuters on Sunday would stay in place until at least July 2016.
Ukrainian Energy Minister Volodymyr Demchyshyn was due to hold a press briefing later on Monday and Ukrenergo's Boska was due to meet with the activists.
(Additional reporting by Lidia Kelly in Moscow; Writing by Alessandra Prentice; Editing by Andrew Osborn and David Stamp)