The government’s support for the militia, which only just swore off violence, has opened new sectarian fault lines in Iraq’s political crisis while potentially empowering Iran at a moment of rising military and economic tensions between Tehran and Washington.

The militant group, Asaib Ahl al-Haq, broke away from the fierce Shiite militia commanded by the anti-American cleric Moktada al-Sadr, who has strong ties to Tehran. The American military has long maintained that the group, led by a former spokesman for Mr. Sadr, Qais al-Khazali, was trained and financed by Iran’s elite Quds Force — something that Iran denies…

Yet, critics worry that Mr. Maliki, facing fierce new challenges to his leadership from Sunnis and even his fellow Shiites, may now be making a cynical and shortsighted play for Asaib’s support. They say Mr. Maliki may use the group’s credentials as Shiite resistance fighters to divide challengers in his own Shiite coalition and weaken Mr. Sadr’s powerful bloc, which draws its political lifeblood from the Shiite underclass.

By doing so, Iraq’s government could embolden a militia with an almost nonexistent track record of peace while potentially handing Tehran greater influence in a country where the United States spent billions of dollars and lost nearly 4,500 American soldiers in nearly nine years of war.