Russia and Ukraine pounded each other with heavy overnight missile attacks as diplomatic efforts faltered, with the White House saying there were no imminent plans for presidents Donald Trump and Vladimir Putin to meet.

Ukrainian officials said on Wednesday that Russian attacks had killed six people, including two children, in Kyiv and the nearby region, and forced power outages nationwide.

Ukraine's military said late on Tuesday that it used Franco-British Storm Shadow air-launched missiles to strike a chemical plant in southern Russia's Bryansk region.

Debris from downed weapons strewed the Ukrainian capital, sparking fires in half its districts, Timur Tkachenko, head of Kyiv's military administration, said on the Telegram messaging app.

Two people were killed in the Kyiv attack, while four, including two children, died in the aftermath of Russian strikes on the surrounding region, Ukraine's emergency service said.

Ten people were rescued from a fire in a high-rise building in Kyiv's district of Dniprovskyi, said Mayor Vitali Klitschko, with a child among the five admitted to hospital across the city.

Officials said fires also broke out in the districts of Desnianskyi, Darnytskyi and Pecherskyi, the last home to the Kyiv Pechersk Lavra monastery, a symbol of Ukrainian spiritual and cultural history.

Ukraine's air force said Russia launched 405 drones and 28 missiles in attacks targeting energy infrastructure, with Ukraine downing 16 missiles and 333 drones.

"All night the enemy struck the country's energy infrastructure," Energy Minister Svitlana Hrynchuk said on Telegram.

In a separate post, the ministry said there were emergency power outages in most regions of Ukraine, as a result of the Russian attack on energy infrastructure, including in the city of Kyiv and the region surrounding it.

In the central region of Poltava, oil and gas facilities were damaged in the Myrhorod district by the Russian attack, the regional governor said.

In the frontline southeastern region of Zaporizhzhia, which has been subject to continued strikes and shelling by Russian forces, 13 people were wounded in overnight attacks, regional governor Ivan Fedorov said on Wednesday.

Russia's Defense Ministry said on Wednesday that its attack on Ukrainian energy infrastructure was a response to Ukrainian attacks on Russian civilian targets.

The ministry also said its forces had captured the village of Pavlivka in Ukraine's southeastern Zaporizhzhia region, as well as Ivanivka village in the neighboring Dnipropetrovsk region.

Putin-Trump summit on hold

Putin and Trump last week agreed to hold a summit in Hungary that the Kremlin said could take place within a couple of weeks.

But following a phone call on Monday between the two countries' top diplomats, the White House said the next day that Trump had no plans to meet Putin "in the immediate future". Trump said he did not want to have a wasted meeting – something Moscow also says it wants to avoid.

Russian officials said, however, that preparations continued for a summit.

"The dates haven't been set yet, but thorough preparation is needed before then, and that takes time," said Kremlin spokesperson Dmitry Peskov. "It's clear that all of this is surrounded by a great deal of gossip, rumors and so on. Much of it is completely untrue. There's no news yet."

"Preparations for the summit are continuing," Russian Deputy Foreign Minister Sergei Ryabkov was quoted as saying. "I don't see any major obstacles."

He added: "It's a difficult process, I admit – but that's precisely what diplomats are for."

Hungary's Prime Minister Viktor Orban also said preparations were ongoing. 

"(Hungarian Foreign Minister Peter) Szijjarto is in Washington. Preparations for the peace summit are continuing. The date is still uncertain. When the time comes, we will hold it," Orban wrote on Facebook.

The delay came after Russia reiterated to the U.S. its previous terms for reaching a peace deal, including that Ukraine cede control of the whole of the southeastern Donbas region, three sources told Reuters.

That amounted to a rejection of Trump's statement last week that both sides should stop at the current front lines – a suggestion that Ukrainian President Volodymyr Zelenskyy said on Wednesday was "a good compromise", while doubting Putin would support it.

Zelenskyy in Scandinavia

Zelenskyy was on Wednesday heading to Norway for talks with Prime Minister Jonas Gahr Store, and then to Sweden, where the government said there would be "an announcement in the area of defense export."

Norway is among Ukraine's biggest suppliers of aid, having pledged $27.4 billion to Kyiv for the period 2023-2030.

"Norway stands by Ukraine in its hopes for a lasting and just peace, as the Ukrainian people deserve," Store said in a statement.

Swedish Prime Minister Ulf Kristersson will discuss a possible export deal at defence industry group Saab, the maker of the JAS 39 Gripen fighter jet, the GlobalEye surveillance aircraft, missile systems, anti-tank infantry weapons and other equipment.

"We will discuss a major possible Swedish export deal," Kristersson said, revealing the two leaders would be "looking at one of the world's absolute best fighter jets", while stopping short of saying whether a Gripen deal was on the day's agenda.

He has previously said that simply donating Gripens to Ukraine is currently not on the cards. This would, however, not preclude an export order to boost Ukrainian air defenses over the longer term.

The possibility of supplying Gripens to Ukraine has been under consideration over the past two years but was put on hold to allow Kyiv to focus on the introduction of American-made F-16 fighters that it began deploying last August.