Iran has threatened Ukraine after accusing it of carrying out an attack on one of its ships in the Caspian Sea. 

Tehran has condemned Ukraine for carrying out the strike on what it claims was a commercial vessel in the Caspian Sea, adding that the explosion killed one sailor and injured another. 

After Ukrainian president Volodymyr Zelensky acknowledged the attack, adding that the Iranian vessel was being used to transport Russian 'military cargo', Iran's foreign minister weighed in. 

In a post to X, Abbas Araghchi tonight said: 'Zelensky has attacked an Iranian commercial vessel, killing a sailor. 

'A blatant UN Charter violation done at Israel's behest to drag Europe into its war. In calls with EU High Rep [sic] [Kaja] Kallas and [Russian] FM [Sergei] Lavrov, made clear that what the freeloader in Kyiv did CANNOT GO UNANSWERED.'

Tehran decried the ​attack on its vessel as an act of aggression and ⁠said it would defend its national interests and security, while accusing Kyiv ​of seeking to expand the war in Ukraine.

The Iranian Foreign Ministry summoned ​Ukraine's chargé d'affaires in Tehran to convey its protest over what it described as a 'hostile and criminal' attack. 

But shortly after Tehran's statement last night, Zelensky said that Kyiv had noted Russia was passing ​on its satellite observations in the Middle East to Iran to enable it to direct ‌strikes ⁠in the region amid its war with the US and its Gulf allies. 

The Ukrainian president, in subsequent remarks posted on X, said Kyiv had recorded ​since the beginning of ​July 'active Russian satellite ⁠surveillance of the Gulf states and US military facilities located there. These images subsequently appear in Iran.'

'At the ​same time, there is a clear correlation between Russia's ​satellite imagery ⁠of these sites and Iranian strikes - both before the attacks, in preparation for them, and afterward, to assess the damage inflicted,' Zelensky said.

He said that on ⁠July ​19 and 20 alone, Russian satellite observation had ​included four air bases: two in Bahrain, one in Jordan and one in Kuwait.

Back in Ukraine, Kyiv came under ballistic missile attack from Russian forces early on Sunday, while other regions suffered bombardments later during the day that killed four people.

Russia, for its part, said four people were killed by a Ukrainian drone strike in the Russian-occupied Ukrainian city of Horlivka.

Ukraine's air force said Russian forces had targeted the capital with ballistic missiles, as explosions rocked the city.

In its morning note, the air force said Russia had launched seven ballistic missiles and 136 drones at Ukraine overnight.

In the northern Ukrainian city of Chernihiv, local authorities said a Russian drone hit a supermarket, killing two people including a 10-year-old child, and wounding three others.

'This is deliberate Russian terror that has no military justification,' Zelensky wrote on Telegram.

In the eastern city of Kharkiv, one person was killed and 12 others required medical attention after a daytime drone attack. 

Meanwhile, a glide bomb attack killed one person and wounded six in the southern city of Zaporizhzhia, which has been under heavy bombardment in recent months.

Kyiv Mayor Vitali Klitschko said one blaze had broken out on the seventh and eighth floors of a multi-storey apartment block in a central district after the overnight missile attack. Three people were wounded in the capital, and images released by the state emergency service showed vehicles in flames.

Zelensky had warned on Friday that Russian attacks were likely over the next 48 hours.

In Horlivka, a city in the Russian-occupied part of Ukraine's Donetsk province, Russian-installed Mayor Ivan Prikhodko said four civilians had been killed in a Ukrainian drone strike, Russia's TASS news agency reported. Prikhodko gave no further details.

On Saturday, Russian-installed authorities accused Ukraine of deliberately attacking civilians after 12 people were killed in a drone attack on a holiday camp in a Russian-held part of Ukraine's Zaporizhzhia region.

Both Russia and Ukraine deny targeting civilians in the war launched by Russia's full-scale invasion in February 2022. 

Thousands of civilians have died, most of them Ukrainians killed in Russian attacks.