MOSCOW—Russia’s state statistical service says the number of deaths nationwide in the first three months of 2021 was more than 25 percent higher than the same period a year ago, and it reported thousands more deaths due to COVID-19 in March than tallied by the country’s coronavirus task force. More than 583,000 people died in January-March of this year in Russia, compared with 460,000 for those same months in 2020, the Rosstat agency said in a report issued Friday. The agency did not provide an explanation for the sharply higher death toll, but critics have suggested that Russian officials underplay the severity of the pandemic in the country. The national coronavirus task force counted more than 12,300 deaths from COVID-19 in March, but Rosstat gave a substantially higher number. The agency said there were 15,003 deaths that month in which coronavirus was the leading cause, along with 2,454 cases in …