US Vice President Joe Biden said Thursday that Iraqi leaders have asserted the country's sovereignty in their war against jihadists and do not want to be "puppets" of Iran or other outside powers.

In last month's battle over the town of Tikrit, Iraqi Prime Minister Haider al-Abadi had insisted that forces fighting the Islamic State group must be under Baghdad's authority and not answer to neighboring Iran, Biden said.

The vice president said media coverage had initially portrayed Shiite militias backed by Iran as "running the show" in the Tikrit offensive.

But after the operation stalled in Tikrit, Abadi "courageously stepped in, making it absolutely clear the Iraqi government, him, as commander in chief, was in charge of this operation," Biden said in a speech at National Defense University in Washington.

At Abadi's request, the United States carried out air strikes against the IS in Tikrit, paving the way for Iraqi security forces to seize control of the town days later, according to Biden.

The events in Tikrit proved to be a crucial test of the government's army and political leaders, showing that Baghdad could uphold its own interests, he said.

Iraq for years has faced sectarian pressures from inside and outside the country but "Iraqis don't want to be drawn into regional conflicts," he said. "They don't want to be owned by anybody."

He added: "They don't want to be puppets dangling on a string of anyone's puppeteering in the region."

The vice president sought to counter criticism at home and abroad of the US-led war effort, in which lawmakers have accused Obama of adopting an overly cautious stance that has created an opening for Iran.

But Biden said critics overstated Iran's role and the IS group's strength on the battlefield.

"The claims do not reflect the circumstances on the ground," he said.

Iraq's new government under Abadi had taken "promising" steps to reach out to Sunnis while Iraqi and Kurdish forces had rolled back the IS group across the country, backed up by US-led air power, he said.

"The jury is still out," he said. "But the momentum is in the right direction."

- IS 'united' Iraqis -

Biden delivered a defense of President Barack Obama's strategy against the IS group before Iraq's prime minister pays a visit to Washington next week.

In appeal to Baghdad, Biden said Iraq's leaders had to continue to pursue reconciliation among the country's Sunni, Kurdish and Shiite communities.

"The entire region is watching this closely. And Iraqi leaders can't afford to lose that sense of political urgency that brought them to this point," he said.

"They must continue to compromise. And it is hard," said Biden, citing years of bloodshed fueled by sectarian violence.

But he said that ironically the IS group's brutal tactics and massacres had helped rally rival leaders to form a new government under Abadi.

He said "the very outfit that intended to tear Iraq apart and establish a caliphate, it actually united the Iraqis."

The Sunnis realized they preferred a new Iraqi government to being at "the mercy" of the IS or "dependent upon the other Sunni states," he said.

The Kurds concluded that pulling out of Iraq was not viable and would mean having a "terrorist state" on its doorstep. And the Shiites did not want to confront the IS jihadists alone or "become a vassal of a neighboring state," he said.

The Tikrit offensive exposed growing tensions between Iranian-backed militias -- which are the largest and most effective of the volunteer units -- and the US-led coalition.

US officials were irked that Baghdad initially had sought to rely on artillery and advice supplied by Iran without inviting the Americans to take part in the Tikrit operation.

Washington made clear that it did not want Iranian-backed groups involved in taking back Tikrit. And the same militias said they wanted no part of an operation with the US military playing a prominent role.