A Ukrainian woman evacuee from Mariupol looks on after arriving at a registration centre for internally displaced people, amid Russia's invasion of Ukraine, in Zaporizhzhia, Ukraine May 3, 2022.
A Ukrainian woman evacuee from Mariupol looks on after arriving at a registration centre for internally displaced people, amid Russia's invasion of Ukraine, in Zaporizhzhia, Ukraine May 3, 2022. Reuters / UESLEI MARCELINO

Scores of civilians, many of them women and children, remained trapped on Thursday in underground bunkers at a steel works, the last Ukrainian holdout in the ruined city of Mariupol, although Russia promised a new lull in fighting to allow them to leave.

A Ukrainian fighter who said he was holed up in the vast Azovstal steel works accused Russian forces of breaching the plant's defences, in violation of Moscow's ceasefire pledge, for a third day.

"Heavy, bloody fighting is going on," said Captain Sviatoslav Palamar, a deputy commander of Ukraine's Azov Regiment, in a video posted online.

"Yet again, the Russians have not kept the promise of a ceasefire and have not given an opportunity for the civilians who seek shelter ... in basements of the plant to evacuate," he said. Reuters could not independently verify his account or where he was speaking.

Ukrainian presidential adviser Oleksiy Arestovych also said fighting had continued in the steel works but gave no details.

Russia's military did not immediately comment.

Ukraine's dogged defence of Azovstal has highlighted Russia's failure to take major cities in a 10-week-old war that has united Western powers in arming Kyiv and punishing Moscow with sanctions.

In what would be a major historic shift sure to infuriate Moscow, Sweden and Finland may shortly decide to join NATO.

Russia's military promised to pause its activity in Azovstal during Thursday daytime and the following two days to allow civilians to leave, after what Ukrainian fighters described as "bloody battles" prevented evacuations on Wednesday. The Kremlin said humanitarian corridors from the plant were in place.

However, nobody from Azovstal was among more than 300 civilians evacuated on Wednesday from Mariupol and other areas in southern Ukraine, the U.N. humanitarian office said.

Pictures released by Russian-backed fighters appeared to show smoke and flames enveloping the Soviet-era Azovstal complex. Ukrainian officials believe around 200 civilians remain trapped along with fighters in a sprawling network of underground bunkers there.

In an early morning address, Ukrainian President Volodymyr Zelenskiy said Ukraine stood ready to ensure a ceasefire.

"It will take time simply to lift people out of those basements, out of those underground shelters. In the present conditions, we cannot use heavy equipment to clear the rubble away. It all has to be done by hand," Zelenskiy said.

Ukraine's military general staff said the assault on the plant included air support.

The chief commander of Ukraine's armed forces said they needed multiple launch rocket systems to defend against resumed Russian cruise missile strikes around the country. Russia has in recent days attacked railways, weapons dumps and fuel depots.

The U.S. Congress is debating an aid package for Ukraine worth $33 billion, largely for weapons. If it gets more supplies, Ukraine could launch a counter-offensive in mid-June, an adviser to Zelenskiy said.

Mariupol, a port city in southeast Ukraine on the Sea of Azov, is now under Russian control apart from the steel works, after a weeks-long siege. It has been an important target in efforts to cut Ukraine off from its coastal grain and metals export routes, as well as to link Russian-controlled territory in the east of the country to Crimea, seized by Moscow in 2014.

"God forbid more shells hit near the bunkers where the civilians are," said Tetyana Trotsak, an Azovstal evacuee among dozens who reached a Ukraine-controlled town this week, describing her two-and-a-half hour walk to get across a short stretch of ground at the plant strewn with rubble.

NATO ENLARGEMENT?

Sweden and Finland, which shares a 1,300-km (819 mile) border with Russia, stayed out of NATO during the Cold War, but Moscow's invasion of Ukraine has prompted them to rethink their security needs.

Russian President Vladimir Putin embarked on the war partly to counter the expansion of the NATO alliance.

Sweeping sanctions from Washington and European allies have hobbled Russia's $1.8 trillion economy while billions of dollars worth of military aid has helped Ukraine frustrate the invasion.

The United States has provided details on the location of Russia's mobile military headquarters, allowing Ukrainian forces to strike those targets and kill Russian generals, the New York Times reported on Wednesday, citing senior U.S. officials.

In response, Russia said such intelligence sharing would not thwart its goals.

Ukrainian officials said they have killed about 12 Russian generals on the battlefield, the newspaper said. The Pentagon and the White House did not respond to Reuters requests for comment on the report.

EU envoys are working to reach a deal this week on phasing out imports of Russian crude oil within six months and refined products by the end of this year. It requires agreement by all 27 EU governments.

The Kremlin said Russia was weighing responses to the plan.

BATTLES

Ukraine and Russia said fighting had been heavy across the south and east over the past day.

Ukrainian authorities reported shelling of towns near a frontline that divides territory it holds in the Donetsk and Luhansk regions from land held by Russian-backed separatists.

The Ukrainian air force said it had downed three Russian cruise missiles and four aircraft, including two Sukhoi fighter jets, while Russia said it had killed 600 Ukrainian soldiers overnight. Reuters could not independently either report.

Russia calls its actions a "special military operation" to disarm Ukraine and protect it from fascists. Ukraine and the West say the fascist allegation is baseless and that the war is an unprovoked act of aggression.

More than five million Ukrainians have fled abroad since the start of the invasion.