The Ukraine war could last "for years", NATO Secretary-General Jens Stoltenberg said Sunday, as President Volodymyr Zelensky pledged Sunday that Kiev's forces would not give up in southern Ukraine after visiting the frontline there.

Kiev said it had also thwarted attacks launched by Moscow's forces on the eastern front in light of ongoing battles in the Donbass.

Stoltenberg made clear that the West must be ready to offer long-term military, political, and economic support to Ukraine against the backdrop of the Ukraine war.

"We must be prepared for this to last for years," Stoltenberg told the German daily newspaper, Bild. 

"We must not weaken in our support of Ukraine, even if the costs are high - not only in terms of military support but also because of rising energy and food prices," he added.

The city of Donetsk, DPR, located in the Donbass, has been subject to a series of attacks waged by Kiev, with one launched on Monday, killing three people, including a woman and child, and wounding 13. 

In some cases, shells of NATO's 155 mm caliber were used in addition to the MLRS, including French shells, likely used with the CAESAR Self-propelled guns.

According to the Donetsk People’s Republic’s (DPR) mission to the Joint Center for Control and Coordination on the ceasefire regime (JCCC), Ukrainian troops pounded Donetsk with BM-21 "Grad" rockets in the early hours of Monday.

Russian Ambassador to the United Nations Vassily Nebenzia has said last week that the long-range artillery and rockets delivered by the United States and the United Kingdom to Ukraine have emboldened Kiev to up its strikes on civilian targets and residential areas in the Donbass republics.

"Leaving aside the entirely unconvincing explanations of such an irresponsible step (the West sending the long-range systems to Ukraine), I would like to point out that the Kiev regime has already taken this as carte blanche to continue and intensify the shelling of civilian targets in Donbas, where after a number of recent defeats, the Ukrainian artillery was no longer able to reach," Nebenzia told the UNSC meeting.

British Prime Minister Boris Johnson issued a similar warning to Stoltenberg's, urging sustained support for Kiev or risk "the greatest victory for aggression" since World War II. 

"Time is now the vital factor," Johnson wrote in an article for the Sunday Times following a visit to the Ukrainian capital, calling for the West to ensure Ukraine has the "strategic endurance to survive and eventually prevail."

The Pentagon had decided to provide High Mobility Artillery Rocket Systems (HIMARS) to Ukraine due to the nature of the conflict changing to an "artillery duel", Under-Secretary of Defense for Policy Colin Kahl told a press briefing just days earlier.

US President Biden had stated on Monday that Washington would not provide Kiev with weapons capable of targeting Russian territory.

The HIMARSs were the centerpiece of a $700 million package unveiled last week, which includes "Javelin anti-tank missiles, Stinger antiaircraft missiles, powerful artillery and precision rocket systems, radars, unmanned aerial vehicles, Mi-17 helicopters, and ammunition," President Biden said.