According to a US military statement "numerous reliable sources" had located "approximately 50 al-Qaida ... terrorists staging weapons at a train station".
US Marine jets destroyed a train station in a town near the Syrian border on Thursday because fighters were storing weapons there, the statement said.
There was no report of casualties from the attack, the third day of strikes in the area in a week.
"Marine F/A-18 jets dropped precision-guided 500lb bombs on the target after 'numerous reliable sources' saw about 50 al-Qaida-linked insurgents using the facility, the statement said.
Iraqi officials said the attack was launched about 0900 GMT against the railway station on the southwest part of Qaim, 320km west of Baghdad.
They said the building was destroyed but had no information on casualties because of military activity in the area.
US aircraft launched attacks against suspected houses in the same area on Saturday and again on Wednesday.