KYIV, Ukraine (AP) -- Russian forces suffered heavy losses in a Ukrainian attack that destroyed a pontoon bridge they were using to try to cross a river in the east, Ukrainian and British officials said in another sign of Moscow's struggle to salvage a war gone awry.
Ukrainian authorities, meanwhile, opened the first war crimes trial of the conflict Friday. The defendant, a captured Russian soldier, stands accused of shooting to death a 62-year-old civilian in the early days of the war.
The trial got underway as Russia's offensive in the Donbas, Ukraine's eastern industrial heartland, seemed to turn increasingly into a grinding war of attrition.
Ukraine's airborne command released photos and video of what it said was a damaged Russian pontoon bridge over the Siversky Donets River in Bilohorivka and several destroyed or damaged Russian military vehicles nearby -- the Ukrainians said they destroyed at least 73 tanks and other military equipment during the two-day battle earlier this week. The command said its troops "drowned the Russian occupiers."
Britain's Defense Ministry said Russia lost "significant armored maneuver elements" of at least one battalion tactical group in the attack. A Russian battalion tactical group consists of about 1,000 troops.
"Conducting river crossings in a contested environment is a highly risky maneuver and speaks to the pressure the Russian commanders are under to make progress in their operations in eastern Ukraine," the ministry said in its daily intelligence update.
In other developments, a move by Finland and, potentially, Sweden to join NATO was thrown into question when Turkish President Recep Tayyip Erdogan said his country is "not of a favorable opinion" toward the idea. He accused Sweden and other Scandinavian countries of supporting Kurdish militants and others Turkey considers terrorists.
Erdogan did not say outright that he would block the two nations from joining NATO. However, the military alliance makes its decisions by consensus, meaning each of its 30 member countries has a veto over who can join.
An expansion of NATO would be a blow to Russian President Vladimir Putin, who undertook the war in what he said was a bid to thwart the alliance's eastward advance. However, in the wake of the invasion of Ukraine, other countries along Russia's flank fear they could be next.
With Ukraine pleading for more arms to fend off the invasion, the European Union's foreign affairs chief announced plans to give Kyiv an additional $520 million to buy heavy weapons.
Ukrainian Defense Minister Oleksii Reznikov welcomed the heavy weapons making their way to the front lines but admitted there is no quick end to the war in sight.
"We are entering a new, long-term phase of the war," he wrote in a Facebook post. "Extremely difficult weeks await us. How many there will be? No one can say for sure."
The battle for the Donbas has turned into a village-by-village, back-and-forth slog with no major breakthroughs on either side and little ground gained. In his nightly address Friday, Ukrainian President Volodymyr Zelenskyy said no one can predict how long the war will last but that his country's forces have been making progress, including retaking six Ukrainian towns or villages in the past day.
Fierce fighting has been taking place on the Siversky Donets River near the city of Severodonetsk, said Oleh Zhdanov, an independent Ukrainian military analyst. The Ukrainian military has launched counterattacks but has failed to halt Russia's advance, he said.
"The fate of a large portion of the Ukrainian army is being decided -- there are about 40,000 Ukrainian soldiers," he said.
The Ukrainian military chief for the Luhansk region of the Donbas said Friday that Russian forces opened fire 31 times on residential areas the day before, destroying dozens of homes, notably in Hirske and Popasnianska villages. He said Russian troops have taken nearly full control of Rubizhne, a city with a prewar population of around 55,000.
In the ruined southern port of Mariupol, Ukrainian fighters holed up in a steel plant faced continued Russian attacks on the last stronghold of resistance in the city. Sviatoslav Palamar, deputy commander of Ukraine's Azov Regiment, said his troops will hold out "as long as they can" despite shortages of ammunition, food, water and medicine.
In this handout photo provided by the Ukraine Armed Forces Thursday, May 12, 2022, dozens of destroyed or damaged Russian armored vehicles on both banks of Siverskyi Donets River after their pontoon bridges were blown up in eastern Ukraine. (Ukrainian Presidential Press Office via AP)
Anna Loboda, 93, a former choir member who fled from Donetsk region, sings a song at Saint Michael monastery, in Odesa, Ukraine, Friday, May 13, 2022. Loboda, who has no family, has been living in the monastery's facility for the elderly since she was brought to Odesa by a neighbour before Russian forces took over her village. (AP Photo/Francisco Seco)
Russian army Sergeant Vadim Shishimarin, 21, is seen behind a glass during a court hearing in Kyiv, Ukraine, Friday, May 13, 2022. The trial of a Russian soldier accused of killing a Ukrainian civilian opened Friday, the first war crimes trial since Moscow's invasion of its neighbor. (AP Photo/Efrem Lukatsky)
Ukrainian servicemen carry bodies of Russian soldiers to load into a railway refrigerator carriage in Kyiv, Ukraine, Friday, May 13, 2022. (AP Photo/Efrem Lukatsky)
A special task force policeman inspects a site after an airstrike by Russian forces in Lysychansk, Luhansk region, Ukraine, Friday, May 13, 2022. (AP Photo/Leo Correa)
People gather to fill cans with water from a firefighters truck in Lysychansk, Luhansk region, Ukraine, Friday, May 13, 2022. (AP Photo/Leo Correa)
An elderly woman carries a can with water after collecting it from a firefighters truck in Lysychansk, Luhansk region, Ukraine, Friday, May 13, 2022. (AP Photo/Leo Correa)
A special task force policemen deliver bags of breads donated to the people who are living inside a basement used as a bomb shelter, during Russian attacks in Severodonetsk, Luhansk region, Ukraine, Friday, May 13, 2022. (AP Photo/Leo Correa)
A part of an apartment is seen at the side of damaged during a heavy fighting buildings in Mariupol, in territory under the government of the Donetsk People's Republic, eastern Ukraine, Thursday, May 13, 2022. (AP Photo)