Russia-Ukraine latest: Kyiv under Russian air attack; Cruise missile violates Polish airspace

America's explanation of the deadly Russia concert hall attack should not be trusted because Washington has still not established who killed President John F Kennedy in 1963, a Russian foreign ministry spokeswoman has said.

Adrienne Watson, the US National Security Council spokeswoman, has said: "ISIS bears sole responsibility for this attack. 

"There was no Ukrainian involvement whatsoever."

But Moscow spokeswoman Maria Zakharova commented: "If only they could sort out the assassination of their own President Kennedy so quickly.

"But no, for more than 60 years, they have not been able to find out who killed him.

"Or maybe ISIS too?

"Or will they delay for another 60 years with specifics, playing with any 'constructive uncertainty'?"

Ms Zakharova, writing on Telegram, also referenced what she called the "financing of the terrorist activities of the Kyiv organised crime group by American liberal democrats".

Russia scrambled a MiG-31 fighter jet following the approach of two US B-1B bombers towards the Russian border over the Barents Sea, the Russian defence ministry has said.

The American aircraft turned away once the MiG-31 had become airborne, the ministry added. 

It was intercepted by Ukrainian defence systems.

Some 18 of 29 Russia-launched missiles were destroyed, as were 25 of 28 attack drones, Ukraine's air force said on Telegram.

Ukraine has increased imports of electricity and halted exports after a series of Russian missile and drone attacks.

"For the current day, electricity imports are forecast at 14,900 megawatt hour (Mwh)," the Ukrainian energy ministry said.

"No exports are expected."

Russia has said its assaults early on Sunday targeted Ukraine's electric power and gas-producing facilities.

Generation and transmission plants were also attacked by Russia on Friday, causing significant blackouts in many regions. 

On Sunday, energy facilities in three Ukrainian regions were targeted.

Russia focused on a critical infrastructure plant in the Lviv region, the ministry said.

"Equipment caught fire and the facility was de-energised," it said. 

"There were no casualties. The consequences are being assessed." 

The ministry added that power lines in the Kyiv region were damaged, with 1,400 households losing power.

The flag on the White House in Moscow - the building that houses the Russian parliament - has been lowered.

Russia is observing a day of national mourning following the attack on a concert hall northwest of the Russian capital.

The assault, in which more than 130 people were killed, has been claimed by an affiliate of Islamic State.

On screens in Moscow there are images of candles and the words "we mourn".

The attack on a concert hall near Moscow was a "vile" act that offends God, Pope Francis has said.

Speaking in St Peter's Square following a Palm Sunday mass, he said his thoughts were with the victims.

"I assure my prayers for the victims of the vile terrorist attack carried out in Moscow, may the Lord receive them in his peace, comfort their families and convert the hearts of those who ... carry out these inhuman actions that offend God," he said.

The attack, which has been claimed by an affiliate of Islamic State, is the deadliest on Russian soil for years. 

More than 130 people were killed.

Russia is observing a day of national mourning. 

Russia struck Ukraine's electric power and gas-producing facilities in a series of missile and drone attacks on Sunday morning, its defence ministry has said.

It used "high-precision weapons", the Interfax news agency reported.

Ukrainian defences destroyed 18 of 29 Russia-launched missiles and 25 of 28 attack drones, Ukraine's air force said on Telegram.

-sky news