KYIV (Reuters) - Russia is targeting Ukrainian rail lines with airstrikes to disrupt the delivery of desperately needed U.S. weapons to the front and complicate military logistics, a Kyiv intelligence source said on Friday.

The United States approved a $61 billion aid package for Ukraine this week and said the first deliveries should arrive in a matter of days, easing acute shortages of artillery shells that have hamstrung Kyiv's forces for months.

As the aid was finalised after six months of congressional wrangling, Russia's defence minister said on Tuesday that Moscow would increase attacks on logistics centres and storage sites holding Western weapons.

On Thursday, Ukrainian rail infrastructure was targeted by Russian strikes in the eastern Donetsk region, northeastern Kharkiv region and central Cherkasy region, the national rail company said.

The attack in Donetsk, which is the main focus of Russia's offensive in the east, killed three electrical mechanics working for the railway company and wounded four more, it said.

In Kharkiv, which borders Russia, a strike hit the railway station in the city of Balakliia, injuring 13 people, including three rail workers, officials said. The town of Balakliia was liberated from Russian forces in 2022.

Ukrainian officials seldom provide detailed statements about strikes on sensitive military targets, but the Ukrainian intelligence source confirmed to Reuters there had been attacks on rail infrastructure aimed at disrupting the supply of weapons.

"Also, the overall complication of our logistics," the source added.

Outnumbering and outgunning Kyiv's forces many times over, Russian troops have had the battlefield momentum since February when they captured the long-time bastion town of Avdiivka.

A U.S. defence official, speaking on condition of anonymity, said on Thursday that the goal of the aid from the United States was to enable Ukraine to regain the initiative.

Kyiv faces manpower shortages on the battlefield and questions linger over the strength of its fortifications along a sprawling, 1,000-km (621-mile) front line.

Russia has periodically attacked rail infrastructure throughout the 26-months invasion.

In April, Ukrzaliznytsia, the railway company, temporarily suspended all deliveries to the southern Black Sea port of Chornomorsk.

It gave no reason for the decisions but Ukrainian media outlets reported that Russian attacks could have damaged railway tracks to the port's cargo terminals.

(Reporting by Tom Balmforth; Additional reporting by Yuliia Dysa; Editing by Andrew Cawthorne)

By Tom Balmforth