The US Treasury Department says the Russian government's oil revenues for the January-to-March period were over 40 percent lower than a year earlier.

The department on Thursday released a report saying a price cap on Russian oil has been successful. The cap is part of sanctions by Western countries against Russia for its invasion of Ukraine.

The report says that before the invasion, oil revenues accounted for 30 to 35 percent of Russia's budget. In 2023, they account for 23 percent.

The situation in Ukraine is expected to be among items on the agenda at the Group of Seven summit that opened on Friday in the western Japanese city of Hiroshima.

Ahead of the summit, a senior official of the administration of US President Joe Biden told reporters that the US and the other G7 countries will unveil new sanctions aimed at isolating Russia economically and weakening its capability to continue the war in Ukraine.

The US government apparently hopes to reaffirm the G7 countries' unity at the summit and further toughen sanctions against Russia.