WASHINGTON - Iran has deployed advanced rockets and missiles to Iraq to help fight the Islamic State in Tikrit, a leading US newspaper reported Tuesday, calling it a significant escalation of firepower and another sign of Tehran’s growing influence in the Arab country.

United States intelligence agencies, according to The New York Times, detected the deployments in the past few weeks as Iraq was marshaling a force of 30,000 troops - two-thirds of them Shia militias largely trained and equipped by Iran.   

 Iran has not yet launched any of the weapons, but American officials say they fear the rockets and missiles could further inflame sectarian tensions and cause civilian casualties because they are not precision guided. Their deployment is another dilemma for the Obama administration as it trains and equips the Iraqi military and security services to help defeat the Islamic State, but unlike Iran is unwilling to commit fighters and advisers who join Iraqi forces in the field.

One senior American military official who tracks classified intelligence reports was cited as saying that Iran had deployed Fajr-5 artillery rockets and Fateh-110 missiles and their launchers. Another senior American military official who also monitors sensitive government reports on Iran said the deployed weapons were similar to the Fajr-5 rockets and Fateh-110 missiles but were slightly different and had different names. The official offered no other details. The C.I.A. declined to comment.

Either way, American officials agreed that the Iranian missiles introduced a new level of advanced weaponry to the battlefield in Iraq, even as some experts questioned their usefulness at this stage in the battle for Tikrit. But the Fajr-5 rockets are the same weapons that Hamas has fired against Israel in recent conflicts. Hezbollah and the Syrian Army have also been using Iranian rockets and missiles for some time, the Times cited military specialists as saying.

The second senior American military official said the Iranian missiles are ‘not a big deal at this point,’ but then quickly added, ‘My concern, as with artillery and other non-precise weapons, is collateral damage if they employ them.’

Appearing before the Senate Armed Services Committee on March 3, Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, alluded to the deployment of the rockets and missiles when he said, ‘This is the most overt conduct of Iranian support, in the form of artillery and other things.’

General Dempsey said that while the involvement of Iranian-backed Shia in Tikrit, a Sunni area, could be ‘a positive thing,’ he voiced concerns that ‘it will only be a problem if it results in sectarianism.’ ‘That sentiment underscored the reality that even though American officials have deep reservations about Iran’s enduring role in Iraq, Iraqis need Iranian help in defeating the Islamic State,’ the newspaper said.

‘Are you concerned that Iran has basically taken over the fight?’ Senator John McCain, a Republican who heads the Armed Services Committee, asked Defence Secretary Ashton Carter at the same March 3 hearing. ‘Sectarianism is what brought us to the point where we are,’ Mr. Carter replied. ‘And so I do look at it with concern. We’re watching it very closely.’

American officials say they believe Iran imported the rockets and missiles for the Tikrit operation because other artillery was not able to reach targets around the city in what has become a difficult, protracted battle. Even after weeks of fighting, Islamic State militants remained dug in on Monday in Tikrit and still controlled parts of the city against the much larger pro-government force.