Russia has launched attacks across Ukraine, killing at least two civilians, in violation of a unilateral, self-declared ceasefire for the Orthodox celebration of Christmas on Saturday.

The attacks came as the US announced it would send Ukraine another $3.75bn of weapons and other aid, including a first shipment of Bradley armoured vehicles known as “tank killers”.

Washington has also urged Italy to provide air defence systems to Ukraine, during a conversation between two top advisers, the newspaper La Repubblica reported.

The new vehicles, along with a similar shipment from Germany and Patriot air defence missiles from both countries, represent a show of western unity with Kyiv, amid speculation that Moscow may be planning a new mobilisation to expand the ranks of the invading army.

Ukraine has said it needs air defence to protect civilian infrastructure targeted by Russia and more military aid to push through Russia’s fortified frontline positions. Senior officials have said they need 600 to 700 infantry fighting vehicles and 300 tanks.

The Ukrainian president, Volodymyr Zelenskiy, praised the US aid as “exactly what is needed”, as fighting raged across the country. Some of the fiercest battles were taking place around the town of Kremina, in Luhansk, Britain’s Ministry of Defence said on Saturday.

Conifer forest provides cover there even in winter, so “both sides are highly likely struggling to accurately adjust artillery fire”.

Pressure in the area is probably part of Russia’s efforts to take the eastern city of Bakhmut, which have been thwarted by Ukrainian forces.

Fighting has destroyed much of the city, and claimed many lives, the latest a 66-year-old man and 61-year-old woman who were killed by shelling; 13 others were injured.

Ukraine’s government had rejected the unilateral ceasefire as a cynical Kremlin move after heavy attacks during celebrations on 25 December and over the new year holiday, which is an important one in Ukraine.

The Russian-installed governor of Sevastopol in Crimea said air defences had shot down a Ukrainian drone, apparently trying to attack the port.

In Kyiv, priests from the Ukrainian Orthodox church held a highly symbolic Orthodox Christmas service in Ukrainian at the 1,000-year-old Pechersk Lavra monastery, one of the most important religious sites in the city.

Overlooking the right bank of the Dnieper River, the cathedral and monastery complex has been a pilgrimage site for centuries.

Until Thursday, it was under the control of the Orthodox church loyal to Moscow, whose priests are widely suspected across Ukraine of harbouring pro-Kremlin sympathies.

Ukraine’s government took over the administration of the complex and allowed the Ukrainian church to use it for the Orthodox Christmas service.

It was the first time in the 31 years of Ukraine’s independence that a service had been held in the Ukrainian language there, and troops in national uniform were among those singing well-known Ukrainian carols.

“It’s a first victory” for Ukraine, said Oksana Abu-Akel, who hailed it as a significant step in the Ukrainian Orthodox church’s efforts to cut ties with Russia after it started the war more than 10 months ago.

“This is the first time in 300 years that there is really our own service here. Every person feels this joy. It is a victory for all Ukrainians,” she told the Associated Press.