Ukraine and Russia have launched drone strikes against each other, officials from both sides say, within hours of the conclusion of the latest round of direct talks aimed at finding a solution after nearly three and half years of war.

Ukrainian drones hit southern Russian Black Sea areas, killing one person, injuring another and hitting an oil storage depot.

Russian forces staged the latest in a series of mass attacks on Ukraine's Black Sea port of Odesa, triggering several fires in residential and other buildings.

Emergency officials in Russia's Krasnodar region on the Black Sea said on the Telegram messaging app that debris from a falling drone struck and killed a woman in Adler district near the resort city of Sochi.

A second woman was being treated in hospital for serious injuries.

The administrative head of the Sirius federal district, south of Sochi, said a drone hit an oil base, but gave no further details.

Russia's Rosaviatsia aviation authority said operations were suspended at Sochi airport for about four hours.

In Odesa, Regional Governor Oleh Kiper said two floors of a multi-storey apartment building had been set ablaze. Other fires broke out on the roof of a two-storey residence, in kiosks and at a petrol station.

Russia has made Ukraine's Black Sea port of Odesa a primary target of recent strikes. - Reuters file

The city's historic centre, a UNESCO World Heritage Site, was also hit, he said.

Negotiators from the two sides had earlier discussed further prisoner swaps at a brief session of peace talks in the Turkish city of Istanbul, but the sides remained far apart on ceasefire terms and a possible meeting of their leaders.

Russian and Ukrainian negotiators met in Istanbul for their first peace talks in more than seven weeks, with Moscow under pressure from US President Donald Trump to strike a deal or face tough new sanctions.

Opening the meeting, Turkish Foreign Minister Hakan Fidan said he hoped the parties would make progress based on documents they exchanged at their last encounter in June in order to "end this bloody war as soon as possible".

"The ultimate goal here is, of course, a ceasefire that will pave the way for peace," Fidan said.

Ukraine wants the meeting to lay the ground for a summit between presidents Volodymyr Zelensky and Vladimir Putin that it sees as the key to any potential breakthrough.

"Ukraine has consistently advocated for a leaders' meeting. We were ready for it yesterday. We are ready today. And we will be ready tomorrow," Ukrainian delegation chief Rustem Umerov wrote on Telegram.

"Such a meeting could unlock real political progress. Russia must demonstrate its readiness."

But the Kremlin played down expectations of any breakthrough in Istanbul.

"Naturally, no one expects an easy road. Naturally, this will be a very difficult conversation. The projects (of the two sides) are diametrically opposed," Kremlin spokesman Dmitry Peskov told reporters.

Previous talks on May 16 and June 2 led to the exchange of thousands of prisoners of war and the remains of dead soldiers. But those meetings lasted less than three hours in total and made no breakthrough towards ending the war that started with Russia's full-scale invasion of Ukraine in February 2022.

Trump has patched up relations with Zelensky after a public row with him at the White House in February, and has lately expressed growing frustration with Putin.

US President Donald Trump says Russia will face tough sanctions if they don't make peace with Ukraine. - Reuters

Last week he threatened heavy new sanctions on Russia and countries that buy its exports unless a peace deal was reached within 50 days, though reaction on financial markets suggested investors were sceptical that he would follow through.

Three sources close to the Kremlin told Reuters last week that Putin, unfazed by Trump's ultimatum, would keep on fighting in Ukraine until the West engaged on his terms for peace, and that his territorial demands may widen as Russian forces advance.

Russia said its forces had captured the settlement of Varachyne in Ukraine's Sumy region, where Putin has ordered his troops to create a buffer zone after Ukraine mounted a shock incursion into Russia last year and held onto a chunk of its territory for months. Reuters could not independently confirm the battlefield report.

In recent weeks, Russian forces have launched some of their heaviest air attacks of the war, focusing especially on the Ukrainian capital Kyiv.

Ukraine has hit back with attacks of its own, and last month inflicted serious damage on Russia's nuclear-capable strategic bomber fleet by smuggling drones close to air bases deep inside the country.

Conflicting demands

Zelensky said earlier this week that the agenda for talks was clear: the return of prisoners of war and of children abducted by Russia, and the preparation of a meeting between himself and Putin.

Putin turned down a previous challenge from Zelensky to meet him in person and has said he does not see him as a legitimate leader because Ukraine, which is under martial law, did not hold new elections when Zelensky's five-year mandate expired last year. Russia also denies abducting children.

The Kremlin said this week it was unrealistic to expect "miracles" from the talks.

At the last meeting, Russia handed Ukraine a memorandum setting out its key demands, including: full withdrawal of Ukrainian forces from four regions of the country that Russia has claimed as its own; limits on the size of Ukraine's military; enhanced rights for Russian-speakers in Ukraine; and acceptance by Kyiv of neutral status, outside NATO or any other alliance.

Ukraine sees those terms as tantamount to surrender, and Zelensky described the Russian stance as an ultimatum.

Ukraine wants an immediate ceasefire, reparations, international security guarantees and no restrictions on its military strength.