Iraqi forces were massing north of Baghdad on Friday, aiming to strike back at Sunni Islamists whose drive toward the capital prompted the United States to send military advisers to stiffen government resistance.

President Barack Obama offered up to 300 Americans to help coordinate the fight. But he held off granting a request for air strikes from the Shi’ite-led government and renewed a call for Prime Minister Nuri al-Maliki to do more to overcome sectarian divisions that have fuelled resentment among the Sunni minority.

Speculation that Maliki might be forced aside was heightened when the country’s senior Shi’ite cleric urged a speedy formation of a new government following the ratification this week of the results of a parliamentary election held in April. […]