In a move likely to draw further retaliation from Russia in a growing trade war,Ukraine on November 23 suspended freight traffic to the annexed Crimea peninsula, which was left in darkness when unknown saboteurs blew up electricity pylons and left Ukrainian flags on the wreckage.

"The cabinet of  ministers temporarily prohibits freight flows on the border between Ukraine and Crimea at the initiative of Prime Minister Arseny Yatsenyuk," the Ukrainian government's press service said via Twitter.

Earlier in the day, media reports said President Petro Poroshenko told Yatsenyuk to look into the imposition of a cargo blockade on the peninsula, which Russia seized with thousands of troops in February 2014 and quickly annexed to international condemnation.

The formal blockade by Kyiv cements the de facto obstruction by Ukrainian nationalist and Tatar activists of truck deliveries to the peninsula since September 20. Despite a recent decrease in hostilities in East Ukraine, the emerging trade war threatens a new cycle of confrontation between Ukraine and Russia.

After Russia said it will introduce a food embargo against Ukraine from January 1 in protest at the EU-Ukraine free trade pact entering force the same day, Yatsenyuk said this would be answered in kind.

"I want to make it clear that Russia's threats of food embargo on Ukrainian commodities from January 1 are getting similar mirror-like response from Ukraine's authorities," TASS news agency quoted the prime minister as saying.

Black-outlook

Meanwhile, Russian authorities in Crimea were still struggling to restore electricity after the attack on power lines two days earlier which left much of the peninsula's population of around 2mn without power and electric light.

Almost a third of Crimea's electricity needs were covered and all socially important facilities including the airport and transport infrastructure were operating normally, Russian Deputy Prime Minister Dmitry Kozak said in comments reported by TASS.

"The situation in Crimea is difficult but not critical," Kozak said. "Locally generated electric energy meets the peninsula's needs by 30%." Rolling outages were affecting many homes, however.

"There are two hours of electricity in the morning and two hours in the evening," a resident of Sevastopol, the base of Russia's Black Sea fleet, posted on Facebook on November 22.

Local authorities introduced a state of emergency and fell back on emergency diesel generators, but most households are receiving power intermittently, if at all. November 23 was declared a holiday in Crimea because of the mass power outage.

The Russian Energy Ministry said Crimea's reserves of petroleum products are sufficient for up to 26 days.

The power line destruction is widely regarded as the work of Ukrainian nationalists and pro-Crimean Tatar activists, who together still maintain the blockade of road supplies to the pensinula and have called for an energy blockade too. The group "Blockade of Crimea" were the first to post online photos of the blown-up pylons with Ukrainian banners, but denied responsibility for the act.

On November 22, clashes also took place at the pylons between activists from Ukraine's Right Sector nationalist movement and Ukrainian paramilitary police, Ukrainian media reported.

Engineers denied access

A spokesman for Ukrainian Tatars in the region said they will prevent Ukrainian engineers from repairing the pylons until 11 missing Tatars were released, after Ukrainian police detailed a number of activists in the southern Kherson region adjoining the Crimea.

"Until our activists - political prisoners - are released, no repair works will be allowed," said Lenur Islyamov, the leader of Tatar protesters who have prevented freight from entering Crimea from Ukraine by road since September. Tatars, who comprise around 15% of the Crimean population, say they have been subject to renewed persecution under the new Russian authorities and that their plight has been traded away in  larger games on the international stage.

The pylon attack comes as Russia now moves closer to the West again in over dealing with the Islamic State in Syria, and following a reduction of hostilities in the rebel conflict in East Ukraine.

Ukrainian authorities, who earn much needed forex revenue from Russia for supplying electric power to Crimea, said they would fix the problem without Russian assistance.

Crimean Prime Minister Sergei Aksyonov called the interruption of power supply a "terrorist act". "No one will bring Crimeans to their knees, we won't allow for negotiations," he said, as quoted by newswires. "We won't let anyone speak to us in the language of blackmail."

Moscow and Kyiv have refrained from commenting on the attack, which coincided with the second anniversary of the November 21 start of mass protests in 2013 that led to the ouster of pro-Russian ex-president Viktor Yanukovych in February 2014.

Kremlin spokesman Dmitry Peskov said only that Russia had not received any information from the Ukrainian side on the time of resuming electric power supply to Crimea.

"We do not have any information on what measures are being taken and when there will be the result and when the electricity supply will be restored," Peskov said while accompanying President Vladimir Putin on a visit to Tehran.

Russia's emergencies ministry is fielding a team of 3,000 employees to "facilitate daily living" in Crimea, Deputy Minister Alexander Chupriyan said, according to RIA Novosti, warning the outage would be protracted.

First Deputy Prime Minister of Crimea Mikhail Sheremet said the peninsula could only supply half of its electric power needs using backup diesel generators and renewable sources such as wind and solar power, TASS reported. Crimean Fuel and Energy Minister Sergei Yegorov on November 22 said there would be rolling power outages in all cities.

The deputy Russian premier Kozak said Russian authorities will step up construction of a power transmission line via the Kerch Strait. The energy link to Crimea project provides for the construction of a power transmission line from the Rostov nuclear power plant in southern Russia to Crimea's capital Simferopol with one of its sections running through the bottom of the Kerch Strait. Its transmission capacity is to reach 300 MW at the start of 2016.

Work also continues on the construction of a bridge over the strait, which will reduce the peninsula's dependency on transport links via the rest of Ukraine. The bridge is not expected to be completed until 2019 at the earliest.