The ayatollah’s comments came shortly after the office of President François Hollande of France announced that French fighter jets had carried out their first attacks on Islamic State targets in Iraq, fulfilling his pledge a day earlier to join the international military campaign against the group.

Image A Rafale fighter at France's Al Dhafra airbase in Abu Dhabi this week. Credit... Taieb Mahjoub/Agence France-Presse — Getty Images

In recent days, a handful of other Iraqi Shiite leaders or militias with closer ties to Iran have made statements expressing more wariness or opposition to the American-led military efforts, and American officials have said the Iranian proxies may be seeking to remind the Western states that Tehran, too, should be taken into account. On Friday, the Iraqi cleric Moktada al-Sadr, another influential voice with ties to Iran, called for a demonstration in Baghdad on Saturday to protest a potential incursion by American ground forces.

But Ayatollah Sistani, considered both independent and uniquely popular here, was more judicious. While he warned Iraqis to guard against foreign interference, he also appeared to endorse the idea that foreign help may be required to successfully engage the Sunni extremists.

“Iraq may be in need of assistance from its friends and brothers to combat black terrorism,” Ayatollah Sistani said. But he insisted that for Iraq, “preserving its sovereignty and independence must be the most important thing and must be taken into consideration.”

He also appealed for intersectarian solidarity in the fight against the extremists by specifically urging support for Dhuluiya, a Sunni town that has held out for months against a siege by the Sunni extremists. “Our brave Iraqi forces should help and defend Dhuluiya,” he said, “because its people are our brothers and they are the sons of our country.”