Crimea has been left without power after several pylons supplying electricity from the Ukraine were "blown up" up overnight.
Four power lines were reportedly toppled, leaving two million inhabitants on the disputed Crimean peninsula without electricity.
Russia has declared a state of emergency in Crimea until power is fully restored, news agency RIA reported.
It was not immediately clear who had damaged the pylons, but a Russian senator described the move as an "act of terrorism" and implied that Ukrainian nationalists were to blame.
Ukrainian authorities have said activists tried to block efforts to repair the pylon, and that the damage seen is likely a result of shelling of explosive devices.
A member of Ukraine's national guard has been killed and more than 90 police officers and members of the national guard have been injured in clashes outside parliament as MPs took part in a controversial vote.
At least four police and national guard were badly hurt when a grenade was lobbed from a crowd of nationalists protesting in Kiev against a draft law to give special status to separatist regions.
Ukraine's national guard said about 90 of its members were hurt, including four seriously, by the blast.
MPs gave their backing to the reforms, which give more powers to Donetsk and Luhansk.
Several police officers and members of the Ukrainian national guard have been injured in a grenade blast in the capital city.
The explosive was thrown from a crowd of nationalist protesters demonstrating outside parliament in Kiev against a draft law to give special status to separatist regions.
A Reuters TV cameraman at the scene said several police were knocked off their feet by the blast, with two treated at the scene for injuries.
Debris recovered from the crash site of flight MH17 in Ukraine may belong to a Russian-made missile system, Dutch investigators have said.
The prosecutors from the joint international criminal investigation believe the fragments are from the BUK surface-to-air missile system.
The debris has been passed to the Dutch Safety Board, which is carrying out the civilian investigation into the July 2014 crash.
All 298 people on board the Malaysia Airlines flight died when the plane downed over territory held by pro-Russian rebels.
US President Barack Obama has told his Russian counterpart that he needs to remove all "troops and equipment" from Ukrainian territory.
In a statement, the White House revealed Vladimir Putin phoned Obama for their first call since February, to discuss the Iran nuclear talks, the "increasingly dangerous situation in Syria", tackling Islamic State extremists and the situation in Ukraine.
Obama reportedly told Putin that Russia must live up to the terms of a ceasefire deal with the neighbouring country, "including the removal of all Russian troops and equipment from Ukrainian territory", the statement added.
European ministers have agreed to extend economic sanctions on Russia over the Ukraine crisis until the end of January 2016, officials say.
US President Barack Obama has said "standing up to Russia aggression in Ukraine" will be among topics on the agenda at the G7 Summit.
He also listed the global economy, the future of the European Union, trade partnerships, combating extremism, and climate change as areas that will also be discussed.
Sir Malcolm Rifkind told ITV News he is "not particularly surprised" that he is among 89 European Union politicians and other senior figures who have been banned from entering Russia.
The former Foreign Secretary said President Putin has "that sort of little tantrum every so often."
I'm not particularly surprised, Mr Putin tends to go in for that sort of little tantrum every so often and they clearly are feeling that the sanctions are having an effect, they are realising that their economy will continue to be damaged unless they approach the Ukraine issue in a diplomatic way, rather than misuse of their military forces.
Former Lib Dem leader Nick Clegg is among 89 European Union politicians and other senior figures who have been banned from entering Russia.Read the full story ›
The European Union and Ukraine have signed a 1.8 billion euro loan deal in an effort to help revive the country's economy.
It requires Ukraine to adopt a series of reforms including anti-corruption measures to remedy structural problems in its economy.
In the first quarter of 2015, Ukraine's economy contracted by nearly 18 percent from the previous year as the country struggled with the impact of unrest in the industrial heartland of the east.