Russian strikes in Ukraine continued as the Kremlin urged Kyiv to resume grain shipments despite a Russian missile attack over the weekend that threatened to derail a key deal aimed at easing a blockade on Ukraine’s ports.

According to Gov. Oleh Sinegubov, Russian forces struck a school and other civilian buildings in the northeastern Kharkiv region, trapping people under rubble. Shellings were also reported in southern Mykolaiv and eastern Dnipropetrovsk, as well as the hard-hit Donbas region.

Russia’s advances in eastern Ukraine have been slowed by Ukrainian forces’ effective use of Himars rocket systems and other Western-supplied weapons, making it much more difficult for Moscow to solidify its occupation in some areas.

On Monday, Russian-backed separatist officials in the eastern Luhansk region, which Russia claimed control of earlier this month, said Ukrainian forces had targeted Alchevsk with five rockets fired from Himars systems overnight.

Ukrainian Defense Minister Oleksii Reznikov stated on Monday that Ukrainian forces have destroyed 50 Russian ammunition depots since acquiring the long-range Himars systems from the United States last month.

“This cuts their [Russian] logistical chains and removes their ability to conduct active fighting and cover our armed forces with heavy shelling,” he said on national television.

As Russia sought to reclaim territory in Kharkiv and Mykolaiv, Ukraine prepared a counteroffensive in the Russian-controlled Kherson region, whose capital Moscow had captured in the early stages of the conflict.

Russia launched a missile attack on Ukraine’s critical grain-exporting port of Odessa on Saturday, just hours after signing an international agreement to ease its blockade of the Black Sea coastline and allow for the safe transport of grain and other foodstuffs needed to avert a global food crisis.

According to a copy of the agreement obtained by The Wall Street Journal, the strike appeared to violate the terms of a United Nations-brokered agreement signed by Russia and Ukraine in Istanbul on Friday, which stated that both countries would refrain from attacking port facilities or civilian ships used for grain transport.

According to the Kremlin, the strike was aimed at military infrastructure.

“This is in no way related to the infrastructure that is used to fulfill the agreements and export grain. Therefore, this cannot and should not affect the start of the shipment process,” Kremlin spokesman Dmitry Peskov said on Monday.

Later Monday, during a visit to the Democratic Republic of the Congo, Russian Foreign Minister Sergei Lavrov stated, “There is nothing in Russia’s obligations that prevents it from destroying military infrastructure.”

Ukrainian officials have vowed to keep trying to export grain that has been piling up in silos along the country’s borders since Russia invaded.

“We continue technical preparations to launch agricultural product exports from our ports,” Ukrainian Infrastructure Minister Oleksandr Kubrakov said after the attack on Saturday. “We will not abandon our goal of opening seaports.”

The attack drew immediate global condemnation from officials who questioned Moscow’s commitment to the agreement and willingness to assist in alleviating food shortages affecting millions of people worldwide.

The attack, according to Secretary of State Antony Blinken, “casts serious doubt” on Russia’s interest in lifting the blockade.

Mr. Peskov urged on Monday that assessments of the agreement be withheld until shipments begin.

Meanwhile, Ukrainian President Volodymyr Zelensky fired Ruslan Demchenko, his first deputy secretary for the National Security and Defense Council, according to a statement issued by his office on Monday. Mr. Demchenko’s dismissal follows the Ukrainian leader’s recent purge of a number of top security and intelligence officials over alleged failures to weed out Russian sympathizers and spies at the heart of his government.

In 2010, Mr. Demchenko lobbied for ratification of the so-called Kharkiv Pact, through which Ukraine agreed to extend the stay of the Russian Black Sea fleet on the Crimean Peninsula. Russia annexed Crimea in 2014.