The statement came yesterday after an official said the US was already providing reconnaissance support for Iraqi forces there, the first confirmation of American involvement in the operation.
Such assistance could help Iraqi forces move forward with their largest operation against IS jihadists to date, which enjoyed initial success but has since stalled into a siege, with the city surrounded but not retaken.
A US-led coalition has targeted IS with air strikes and provided training and equipment to Iraqi forces, but had not previously announced direct assistance for the Tikrit operation, in which Iran has played a major role.
The delicate diplomatic and military aspects of such an option are still being worked out, said the official, who spoke on condition of anonymity.
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In a shift, the coalition as of March 21 began providing intelligence from surveillance flights for the Tikrit assault, a senior coalition military official said earlier in Baghdad.
US officials in Washington confirmed the account of "an eye in the sky" for the Iraqi troops and Iranian-backed Shiite militia.
President Barack Obama's administration has insisted it does not coordinate military operations directly with Iran.
IS led a sweeping offensive last June that overran large areas north and west of Baghdad, including Tikrit, the capital of Salaheddin province and executed dictator Saddam Hussein's home town.
Iraqi security forces initially fared poorly against IS, with multiple divisions collapsing in the north, but have since made major gains against jihadists with the aid of tens of thousands of allied paramilitaries, the US-led coalition and Iran.