Iraqi forces’ operation to retake the city of Tikrit has stalled as troops suffer heavy casualties at the hands of Islamic State militants, raising concerns about whether the pro-government fighters are ready for major offensives.

After two days of little activity on the battlefield, Iraq’s interior minister, Mohammed al-Ghabban, confirmed Monday that the offensive has “temporarily stopped.” The steady flow of coffins arriving in Iraq’s Shiite holy city of Najaf suggests a reason for the pause; cemetery workers say as many as 60 war dead have been arriving each day.

Since last week, Iraqi forces have hemmed in the Sunni militants in Tikrit, claiming control of the majority of the former Islamic State stronghold. But the operation has come at a cost, with soldiers saying the fight has been tougher than expected. As the momentum has slowed, some Iraqi officials have begun to publicly call for U.S.-led air support. […]