KYIV, Ukraine >> Russian forces launched a deadly strike in eastern Ukraine on Saturday as President Volodymyr Zelenskyy marked the 500th day of the war with a show of defiance, sharing a video of himself visiting a Black Sea island that has become a potent symbol of his country’s resistance to the invasion.

In the kind of attack that has become painfully familiar, at least seven civilians were killed and 13 others were injured when Russian forces shelled the city center of Lyman in the eastern Donetsk region at around 10 a.m., Ukrainian officials said.

Russian forces used cluster munitions in the attack, according to Ukraine’s prosecutor general.

At the scene of the strike were bloodstains, shattered glass and an overturned motorcycle. The midmorning assault was a reminder of the toll taken on Ukraine by 500 days of war. Zelenskyy paid tribute Saturday to all those who have lost their lives, using the backdrop of Snake Island to underscore Ukrainian resolve. At the start of the war in February 2022, an audio recording captured Ukrainian border guards on the island, 20 miles off the coast of Odesa. Defying an order by a Russian warship to surrender, the guards responded with a memorable burst of profanity that became a rallying cry immortalized on stamps and on billboards around the country.

In the video posted Saturday, Zelenskyy honored the “heroes” who fought for Snake Island, calling the battle that ultimately forced Russian troops to withdraw last June “one of the most important” since the full-scale invasion.

“Although this is a small piece of land in the middle of our Black Sea, it is a great proof that Ukraine will regain every bit of its territory,” Zelenskyy said in the video, which showed him clambering off a boat and across a rocky landscape to lay blue and yellow flowers at a memorial.

It was not immediately clear when the video was filmed: The Ukrainian leader was still in Turkey on Saturday, a trip described in part as an effort to drum up support for his country’s bid to join NATO.

But in keeping with the theme of defiance, he left Istanbul on Saturday with something of immense personal and symbolic value to many Ukrainians. Zelenskyy said on Twitter that five commanders from the country’s Azov Battalion, who defended the port city of Mariupol last year during an 80-day Russian siege, would be returning home with him.

The fighters’ fierce resistance from inside a sprawling steel plant made them national celebrities but also a valuable prize for the Kremlin when they surrendered to Russian forces in May. They later were sent to Turkey in a prisoner swap negotiated by Ankara. Zelenskyy repeatedly had pledged to secure their release along with all Ukrainian prisoners of war.

“We are returning home from Turkey and bringing our heroes home,” he wrote Saturday on Twitter, sharing a video that showed him embracing the five men, who later were shown a phone with the footage from Snake Island.

The move was a symbolic climax to a week of diplomatic meetings that ended in Turkey, part of a tour of NATO countries before the alliance’s summit this week.

The war has reshaped Ukraine’s relationship with the world, adding momentum to its bid to join NATO and turning Zelenskyy into a diplomatic juggernaut. He has used the global attention to help Ukraine push for billions in military aid to fend off Russia, and his country, armed with Western-supplied weapons, is in the early stages of an intensely scrutinized campaign to take back occupied territory.

Kyiv views membership in NATO as the ultimate guarantee of its security; its application in September to join the alliance was made against the backdrop of Russia’s full-scale invasion.

While Zelenskyy has acknowledged that Ukraine won’t be joining NATO any time soon, given that such a move would force the mutual defense alliance into direct military conflict with Russia, he repeatedly has urged its members to set out a timetable for accession. In recent months, he has expressed hope that this week’s summit in Vilnius, Lithuania, could provide clarity.