At least 15 people were killed and 20 more were injured Sunday in a Ukrainian missile strike on an apartment block in the Russian border town of Belgorod.

In one of the deadliest attacks to date on the region, Ukraine launched what Russian officials said was a massive missile attack, involving Tochka ballistic missiles and Adler and RM-70 Vampire (MLRS) multiple-launch rocket systems.

Footage from the scene showed at least 10 stories of the building collapsing. Later, as emergency services scoured the rubble for survivors, the roof collapsed and people ran for their lives, dust and rubble falling behind them.

Russia's Defense Ministry said the attack, which it called a "terrorist attack on residential areas," took place at 08.40 a.m. GMT and involved at least 12 missiles.

"Fragments of one of the downed Tochka-U missiles damaged an apartment building in the city of Belgorod," the ministry said.

Russia's emergency ministry said early on Monday that 15 people were killed. Russian news agencies said that 20 people were injured and at least one child was among the missing. Rocket sirens went off as emergency workers searched the rubble.

Both Ukraine and Russia say they do not target civilians in the war, which Russia launched at its smaller neighbor in February of 2022. The war has killed thousands, displaced millions and turned Ukrainian cities into rubble.

The Kremlin said President Vladimir Putin had been briefed on the attack, which it said was "barbaric." Russia's Foreign Ministry said the targeting of civilians and civilian infrastructure was criminal.

There was no immediate comment from Ukraine. Kyiv says that targeting Russia's military, transport and energy infrastructure undermines Moscow's war effort and is an answer to the countless deadly attacks by Russia.

Deep into Kharkiv

After heavy shelling of Ukraine's northeastern Kharkiv region, Russian forces smashed through the border over recent days and say they have pushed Ukrainian forces out of at least nine villages in the area.

The move opens up a new front and has forced Ukraine to dedicate additional troops to the area just as Russian forces advance at key points along the front in the south and the east.

Russian troops said Sunday they seized another four villages – Hatyshche, Krasne, Morokhovets and Oliinykove – in Ukraine's Kharkiv region.

Russian military bloggers said Russia was taking advantage of its numerical superiority to push hard into relatively undefended areas with small highly mobile units of troops, which then surrounded Ukrainian positions.

Ukraine's military chief said his country's forces were facing a difficult situation in fighting in the Kharkiv region, but that they were doing all they could to hold the line.

In response to Ukrainian attacks on Belgorod, Putin suggested in March that Moscow could try to establish a buffer zone inside Ukrainian territory.

The conflict in eastern Ukraine began in 2014 after a pro-Russian president was toppled in Ukraine's Maidan Revolution, and Russia annexed Crimea, with Russian-backed separatist forces fighting Ukraine's armed forces.

About 14,000 people were killed there between 2014 and the end of 2021, according to United Nations High Commissioner for Human Rights (OHCHR), including 3,106 civilians.