KYIV, Oct 11 ― Ukraine vowed to strengthen its armed forces after Russia launched its biggest aerial assaults on cities since the beginning of the war, forcing thousands to flee to bomb shelters and prompting Kyiv to halt electricity exports to Europe.

Missiles hit cities across Ukraine yesterday morning, killing 12 people and injuring scores, as they tore into intersections, parks and tourist sites.

Explosions were reported in Kyiv, Lviv, Ternopil and Zhytomyr in western Ukraine, Dnipro and Kremenchuk in the centre, Zaporizhzhia in the south and Kharkiv in the east, Ukrainian officials said.

The barrage of dozens of cruise missiles fired from air, land and sea was the most widespread wave of air strikes to hit away from the front line, at least since the initial volleys on the war's first day, February 24.

Russian President Vladimir Putin ordered "massive” long range strikes after an attack on the bridge linking Russia to the annexed Crimean peninsula over the weekend, and threatened more strikes in future if Ukraine hits Russian territory.

Ukraine's Volodymyr Zelensky spoke to US President Joe Biden on Monday and wrote on Telegram afterwards that air defence was the "number 1 priority in our defence cooperation.”

"We will do everything to strengthen our armed forces,” he said in a Monday night address. "We will make the battlefield more painful for the enemy.”

Biden told Zelensky the US will provide advanced air defence systems. The Pentagon said on September 27 it would start delivering the National Advanced Surface-to-Air Missile System over the next two months or so.

Moscow's attacks caused thousands of Ukrainians to race to bomb shelters as air raid sirens rang out.

Zelensky said 12 people were killed and officials have reported scores of injured after the assaults.

The attacks were deliberately timed to kill people and knock out Ukraine's power grid, he said. His prime minister reported 11 major infrastructure targets were hit in eight regions, leaving parts of the country with no electricity, water or heat.

As it tried to end blackouts, Ukraine halted electricity exports to the European Union, at a time when the continent already faces surging power prices that have stoked inflation, hampered industrial activity and caused sky-high consumer bills.

The president of the United Arab Emirates, a member of the group of oil producers known as Opec+ that rebuffed the US last week by announcing steep cuts last week, will travel to Russia today to meet with Putin and push for "military de-escalation”, UAE state news agency WAM reported.

Battlefield setbacks

The Kremlin's air strikes come three days after a blast damaged the bridge it built after seizing Crimea in 2014. Russia blamed Ukraine and called the deadly explosion "terrorism”.

"To leave such acts without a response is simply impossible,” said Putin, alleging other, unspecified attacks on Russian energy infrastructure.

Ukraine, which views the bridge as a military target sustaining Russia's war effort, celebrated the blast without claiming responsibility.

With troops suffering weeks of setbacks on the battlefield, Russian authorities have been facing the first sustained public criticism at home of the war, with commentators on state television demanding ever tougher measures.

Since early September, Ukrainian forces have burst through front lines and recaptured territory.

Putin responded by ordering a mobilisation of hundreds of thousands of reservists, proclaiming the annexation of occupied territory and threatening repeatedly to use nuclear weapons.

On Saturday, Russia's Defence Ministry named General Sergei Surovikin, who won acclaim in Syria, as commander of Russian forces in Ukraine. A Russian air campaign in Syria helped the government crush its enemies.

Russia says it is waging a "special military operation” in Ukraine to rid it of nationalists and protect Russian-speaking communities. Ukraine and the West describe Russia's actions as an unprovoked war of aggression.

Monday's blasts tore a huge crater next to a children's playground in one of central Kyiv's busiest parks. The remains of an apparent missile were buried, smoking in the mud. More volleys struck the capital again later in the morning.

Ukraine's defence ministry said in its evening update Russia had staged at least 84 missile and air strikes, and Ukraine's air defences had destroyed 43 cruise missiles and 13 drones.

Russia's defence ministry said it had hit all its intended targets.

Reuters could not independently verify battlefield accounts.

Ukraine's Prime Minister Denys Shmyhal promised to restore utilities as quickly as possible.

In another sign of possible escalation, Putin's closest ally, President Alexander Lukashenko of Belarus, said he had ordered troops to deploy jointly with Russian forces near Ukraine, which he accused of planning attacks on Belarus with its Western backers.

Russia used Belarus as a staging ground early in the war but Lukashenko has not sent in his troops. ― Reuters