Ukraine’s long-awaited southern counteroffensive has started, a representative for the country’s southern military command said on Monday, as Kyiv’s forces attempted to punch through Russian lines around the southern city of Kherson.

Natalia Humeniuk, spokesperson for Ukraine’s Operational Command South, told Ukrainian media that the country’s armed forces “have started offensive actions in various directions,” and in particular toward the southern region of Kherson, which was occupied by Russian forces early in the war.

The city of Kherson holds a vital strategic position on the Dnieper River and Black Sea.

According to local reports, Ukrainian forces launched their counterattack overnight. Kherson authorities have called on residents to seek shelter and stock up on food and water.

Humeniuk refused to reveal the targets of the counteroffensive. In a statement to CNN, she said details would be available after the operation is complete.

She also urged people to remain silent on the attack: “Any military operation requires silence. In the conditions of a hybrid war, such a reaction to news from the front harms the armed forces.”

Russian news agency RIA reported that shelling by Ukrainian forces destroyed a secondary school and houses in the city of Beryslav in the Kherson region, and that residents were seeking shelters in another city across the river.

While the fighting has intensified in recent weeks, Ukraine’s counteroffensive has long been expected.

It comes as a team from the U.N.’s International Atomic Energy Agency is heading to the Zaporizhzhia nuclear power plant on Monday. Fierce fighting between Russian and Ukrainian forces in the vicinity of the nuclear plant have raised fears of a nuclear disaster.