US President Donald Trump is pushing for a rapid end to the three-year war and hopes the talks in Riyadh can pave the way to a breakthrough, but the Kremlin has warned of "difficult negotiations" ahead.

Despite both warring sides proposing different plans for temporary ceasefires, attacks have continued unabated.

Originally scheduled to take place simultaneously to enable shuttle diplomacy -- with the US going back and forth between the delegations -- the technical-level talks on a partial truce are now taking place separately, one after the other.

The meeting between the Ukrainian team, led by defence minister Rustem Umerov, and the Americans finished up late Sunday night, Umerov said.

"The discussion was productive and focused -- we addressed key points including energy," he said on social media, adding Ukraine was working to make its goal of a "just and lasting peace" a reality.

Umerov had previously said proposals to protect energy facilities and critical infrastructure would be on the agenda.

In an evening address, Ukrainian President Volodymyr Zelensky said that "Russia is the only one who is dragging this war out".

"No matter what we talk about with our partners, we need to push Putin to give a real order to stop the strikes: the one who brought this war must take it away," he said.

Discussions between the United States and Russia were set for Monday, with Russian state media reporting Moscow's delegation had arrived in Riyadh on Sunday.

Trump envoy Steve Witkoff voiced optimism that any agreement struck would pave the way to a "full-on" ceasefire.

"I think you're going to see in Saudi Arabia on Monday some real progress, particularly as it affects a Black Sea ceasefire on ships between both countries. And from that you'll naturally gravitate to a full-on shooting ceasefire," he told Fox News.

But the Kremlin on Sunday downplayed expectations of a rapid resolution, saying talks were just beginning.

"We are only at the beginning of this path," Kremlin spokesman Dmitry Peskov told Russian state TV.

He said there were many outstanding questions over how a potential ceasefire might be implemented.

Russian President Vladimir Putin has rejected a joint US-Ukrainian call for a full and immediate 30-day pause, proposing instead a halt in attacks only on energy facilities.

"There are difficult negotiations ahead," Peskov said in the interview, published on social media.

- Black Sea -

Peskov said the "main" focus in its talks with the United States would be a possible resumption of a 2022 Black Sea grain deal that ensured safe navigation for Ukrainian farm exports via the Black Sea.

"On Monday, we mainly intend to discuss President Putin's agreement to resume the so-called Black Sea initiative, and our negotiators will be ready to discuss the nuances around this problem," Peskov said.

Moscow pulled out of the deal -- brokered by Turkey and the United Nations -- in 2023, accusing the West of failing to uphold its commitments to ease sanctions on Russia's own exports of farm produce and fertilisers.

A senior Ukrainian official previously told AFP that Kyiv would propose a broader ceasefire, covering attacks on energy facilities, infrastructure and naval strikes.

Both sides launched fresh drone attacks on the eve of the negotiations.

Ukrainian officials said a Russian drone attack killed three civilians in Kyiv, including a five-year-old girl and her father.

AFP reporters in the capital saw emergency workers treating the wounded in the early hours of Sunday in front of damaged residential buildings hit in the strike.

Deadly strikes on the well-protected city are rarer than elsewhere in the country.

Ukraine's air force said Russia launched 147 drones at the country in the latest barrage.

- 'Mutually beneficial' -

Zelensky urged his country's allies to put fresh pressure on Russia.

"New decisions and new pressure on Moscow are needed to bring an end to these strikes and this war," he posted on social media on Sunday.

Russia said it had repelled nearly 60 Ukrainian drones overnight.

Officials said one man was killed in the southern Rostov region of Russia when his car was set alight by falling drone debris, and a woman was killed in the Belgorod border region, also by a drone attack.

Ukraine's army, meanwhile, said it had captured a small village in its eastern Lugansk region, a rare battlefield success for Kyiv's struggling forces.

Moscow heads into the Saudi talks after a rapprochement with Washington under Trump that has boosted confidence in the Kremlin.

Peskov said on Sunday that the "potential for mutually beneficial cooperation in a wide variety of spheres between our countries cannot be overstated".

"We may disagree on some things but that does not mean we should deprive ourselves of mutual benefit," he added.