Iran appears to have fired only a single missile on Thursday, not a second round of missiles as suggested by Iranian media reports, a senior US defense official said.
The official, who spoke on condition of anonymity, told AFP the United States had detected the launch of seven missiles on Wednesday, including a Shahab-3 missile said to be capable of striking Israel.
"There appears to have been one missile fired today, but that may well have been one that failed the day before, and they finally got operational and launched today," the official said.
A second US official, who also spoke on condition of anonymity, said there was a "second firing" on Thursday or late Wednesday "but it was much smaller than the first."
"These are the kinds of things that it does take time to look at," the official cautioned.
Pentagon press secretary Geoff Morrell said the Iranian missile shots were intended as "a show of force to intimidate their neighbors" rather than a test of new capabilities.
"This operation seems much less about testing than trying to flex their muscles in public," he said.
"All these capabilities had been tested before. This appears to be much more for impact on the public than it was an attempt to test these capabilities," he said.
At the same time, however, Morrell said the missile shots showed that Iran is bent on developing missiles capable of striking Israel "and indeed our friends in Europe."
Administration officials have said the display of Iranian firepower nonetheless underscores the need for a missile defense system in Europe.
The US missile defense system proposed for Poland and the Czech Republic, however, is designed to counter longer-range missiles than the Shahab-3, which Iran does not currently possess.
The Shahab-3 is advertised as having a 2,000 kilometer range (1,250 miles), which would put Israel, Saudi Arabia, and US military installations throughout the Middle East within striking distance -- but not Europe.
