Russian forces advanced deep into the ruined eastern factory city of Sievierodonetsk on Friday, but Ukrainian troops resisted as Russia’s assault on its neighbor entered its 100th day.

Ukraine’s defense minister said his troops were already training in Europe to operate new, advanced missile systems pledged this week by the US and Britain, which Kyiv hopes will tip the balance of power in its favor.

A war that Western countries believe Russia intended to end in hours has dragged on for more than three months, with Moscow driven back from the capital but launching a massive new offensive in the east.

On Thursday, Reuters arrived in Sievierodonetsk and confirmed that Ukrainians still controlled a portion of the city. Troops drove at high speed towards a plume of black smoke, over roads littered with wrecked armored vehicles. One soldier sat in the back seat, his face bloodied from injuries.

Ukrainian troops, including foreign volunteers, were unloading weapons from a truck in another part of town.

Russia has poured its forces into the battle for Sievierodonetsk, which is known for its large chemical factory and which Russia must capture in order to achieve its stated goal of holding all of Luhansk province. Both sides have suffered crushing losses in a street-by-street battle that could set the stage for a protracted war of attrition. He claimed that roughly one-fifth of the city was now a contested “grey zone.” Ukrainian fighters were able to clear Russians from some streets while holding out in one area. He claimed they had captured six Russian prisoners the day before.

Ukrainian forces had some success in the city overnight, according to Defense Minister Oleskiy Reznikov, though he said it was too early to provide details.

Russian troops were stationed just 15 kilometers (9 miles) outside the city of Sloviansk in neighboring Donetsk province, another key target of Moscow’s eastern offensive, regional governor Pavlo Kyrylenko said.

Donetsk will not fall quickly, but more weapons are needed to keep the attackers at bay, according to Kyrylenko. Defense Minister Reznikov said via video link to a security conference in Bratislava that Ukrainian artillery crews were being trained to operate new HIMARS and MLRS rocket systems.

Washington said this week that Ukrainians would need three weeks of training before using the rockets, which have a range of up to 80 kilometers (50 miles) and could hit Russian rear supply lines, helping to negate Russia’s artillery firepower advantage at the front.

Despite being driven from the north of Ukraine in March following a failed assault on the capital, Russia still controls roughly one-fifth of the country, with roughly half seized in 2014 and the other half captured since the invasion began on Feb. 24.

The recent Russian offensive in the east has been one of the bloodiest phases of the war for both sides. Moscow has made slow but steady progress, squeezing Ukrainian forces into a pocket in the provinces of Luhansk and Donetsk, but has yet to encircle them.

Meanwhile, Kiev hopes that the Russian advance will deplete Moscow’s forces, allowing Ukraine to launch counter-offensives and recapture territory in the coming months.

Resnikov expressed hope that Russian forces would be driven out of eastern Ukraine this year, but he did not have “tarot cards” to predict when.

After the latest $700 million US weapons package for Ukraine, President Volodymyr Zelenskiy said in an overnight address that Kyiv was expecting more “good news” on foreign weapons.

According to President Joe Biden’s administration, Ukraine has promised not to use the new rockets to target Russian targets. Moscow, which describes its invasion as a “special military operation” to disarm Ukraine and rid it of dangerous nationalists, claims Western weapons will “feed the fire.”

The war has had a devastating effect on the global economy, particularly in poor countries that rely on food imports. Ukraine is one of the world’s leading suppliers of grain and cooking oil, but the closure of its Black Sea ports cut those supplies off the market.