Toyota is recalling a total of 778,000 RAV4 and Lexus HS 250h models sold in the United States to fix a problem in the rear suspension that it says arises when the vehicles are serviced.

The recall involves 760,000 RAV4s from the 2006 to early 2011 model years and 18,000 Lexus HS 250hs from the 2010 model year.

The recall, announced on Wednesday, follows the investigation begun in June by the National Highway Traffic Safety Administration into possible suspension failures involving some 460,000 RAV4s from 2006-8.

In its news release, Toyota said its own investigation had determined “that if the nuts on the rear suspension arm are not tightened following the proper procedure and torque specification during a rear-wheel alignment service, excessive play may occur at the threaded portion of the arm, followed by rust formation.”

If rust builds up, “threads may wear, causing the arm to separate, which could result in loss of vehicle control,” Toyota wrote in a report to the safety agency on Wednesday.

“In the United States, there are nine crashes and three minor injuries alleged to be related to this condition,” a Toyota spokesman, Brian R. Lyons, said in an e-mail.

Toyota concluded in July that the issue was caused by the “improper tightening of the lock nut during adjustment of a rear-wheel alignment in the field,” according to its letter to the agency. Toyota added that it decided to announce a recall “to ensure proper tightening of the lock nuts.”

The automaker said it was developing a remedy to fix the defect, which was not present in any other Toyota or Lexus vehicles.

In June, N.H.T.S.A. said that its Office of Complaints had received seven complaints about corrosion-related failure of the left or right rear suspension arm on RAV4s. Four complaints said the failure occurred while driving at at 35 m.p.h. or greater, causing a temporary loss of vehicle control.

Toyota said it received a complaint in May of a customer who “alleged loss of vehicle control, while driving on the highway, resulting in an accident.”

The automaker said it inspected and analyzed the scene of the accident and the vehicle. As a result, Toyota said in its letter to the agency that it found “the left arm separated at the outer side of the turn-buckle.”

It said it could not determine when that failure happened. “However, according to the customer’s allegation that a loud noise was heard before the vehicle swerved, the arm could have separated before the accident.”

Toyota concluded that improper service during a rear-wheel alignment might have caused the issue to develop, leading to the recall.