A spokesman said the missiles would help counter the threat from large IS car bombs in the city, west of Baghdad.
Iraqi forces are regrouping and are expected to retake the city in the "near term", Col Pat Ryder said.
More than 40,000 people have fled their homes since IS militants seized the Ramadi last Friday.
On Wednesday, thousands displaced by the violence in the western province of Anbar were finally allowed to enter Baghdad.
Many had been stranded on open land for several days amid government fears that IS might have infiltrated them.
Residents still left in Ramadi told the Associated Press news agency that IS fighters were urging them over loudspeakers not to be afraid and to stay in the city.
According to Anbar provincial officials, at least 500 people were killed in three days of fighting in Ramadi last week.
Col Ryder described the waves of "vehicle-borne improvised explosive devices" (VBIEDs) used by IS in their offensive as "devastating".
"These enormous suicide VBIEDs is something that we have to help the Iraqis, and our partners in Syria, defeat," he said.
Iraqi troops in the area are expected to launch an attack on IS soon and they could be joined by about 3,000 Shia militia fighters.
But the BBC's Gary O'Donoghue in Washington says the US insists it will only provide air cover to fighters under the control of the Iraqi government - reflecting concerns that some of the groups are controlled by Iran.
Meanwhile, Iraqi Prime Minister Haider al-Abadi flew to Russia on Wednesday, seeking closer military co-operation.
Mr Abadi, who is travelling with a large number of ministers and advisers, is due to meet Russian President Vladimir Putin on Thursday.
Changing fortunes in Iraq put Obama legacy at risk
The US military says it is sending 1,000 anti-tank missiles to the Iraqi government following the fall of Ramadi to Islamic State (IS) forces.