TIKRIT, Iraq — The commander of Iraq's powerful Shiite militias accused the U.S. of falling short on promises to help Iraq in its battle against the Islamic State group and called Iranian assistance to Iraqi security forces "unconditional."

In an interview on the battlefield near the Iraqi city of Tikrit Friday, Hadi al-Amiri, who is also head of the Badr Organization political party, criticized those who "kiss the hands of the Americans and get nothing in return," adding that "help from Iran is unconditional."

Iraqi forces entered Tikrit for the first time on Wednesday from the north and south. On Friday, they fought fierce battles to secure the northern Tikrit neighborhood of Qadisiyya and lobbed mortars and rockets into the city center, still in the hands of IS. Iraqi military officials have said they expect to reach the center of Tikrit within two to three days.

The Iranian-backed Shiite militias have played a crucial role in regaining territory from the Islamic State group, supporting Iraq's embattled military and police forces in battle. An Iraqi government official told The Associated Press that Iran sold Iraq nearly $10 billion worth of weapons and hardware, mostly weapons for urban warfare like assault rifles, heavy machine-guns and rocket launchers. He spoke anonymously as he was not authorized to brief the media.

In November, President Obama authorized the deployment of up to 1,500 more American troops to bolster Iraqi forces, which could more than double the total number of U.S. forces to 3,100. The Pentagon has made a spending request to Congress of $1.6 billion, focusing on training and arming Kurdish and Iraqi forces. According to a Pentagon document prepared in November, the U.S. is looking to provide an estimated $89.3 million worth of weapons and equipment to each of the nine Iraqi brigades.

The U.S.-led coalition of eight countries has launched more than 2,000 airstrikes to date in Iraq alone, and the U.S. is also striking the militant group from the air in Syria. Iraqi and U.S. officials have acknowledged the role airstrikes have played in rolling back the militant group — saying they were an essential component in victories at the Mosul Dam, in Amirli, and more recently, in the crucial oil refinery town of Beiji.

But the U.S. is not taking part in the operation in Tikrit; U.S. officials say they were not asked by Iraq to participate.

Al-Amiri warned that Iraq should not sacrifice its sovereignty for the sake of receiving weapons and assistance from the U.S., suggesting that the Iraqi government is taking instructions from Washington.

"Our sovereignty is more important than U.S. weapons," he said. "We can bring weapons from any country in the world."