General Motors' new electric car, the Chevrolet Volt, is being probed by the US government after battery pack fires.
The National Highway Traffic Safety Administration (NHTSA) is investigating the car, due to be launched in the UK next year, after a lithium-ion battery pack caught fire after a government crash test and another recently crash-tested battery emitted smoke and sparks.
GM said the Volt "is safe and does not present undue risk as part of normal operation or immediately after a severe crash".
The latest fires follow a battery fire in a crash-tested Volt six months ago.
NHTSA learned of a possible fire risk involving damaged Volt batteries when a fire erupted in a Volt that was being stored in a car park at a test centre in Burlington, Wisconsin.
The fire was severe enough to cause several other vehicles parked nearby to catch fire.
The car had been subjected to a side-impact crash test more than three weeks earlier, during which the battery was punctured and its coolant line ruptured.
Last week's tests of three battery packs were designed to replicate the May test, in which the Volt was subjected to a simulated side-impact collision into a narrow object like a tree or pole followed by a rollover, the agency said.
The first battery tested last week did not catch fire, but a battery test last month initially experienced a temporary temperature increase, and this week caught fire.
Another battery tested last month began to smoke and emit sparks shortly after the rotation.
NHTSA and the Energy and Defence departments conducted the tests at a defence facility near Hampton Roads, Virginia.
After the first battery fire, GM officials complained that NHTSA did not drain the battery of energy as called for under the car maker's crash procedures.
NHTSA normally drains fuel from petrol cars after crash tests, they said.
So far no fires have been reported in Volts involved in road crashes, NHTSA said. More than 5,000 of the vehicles have been sold.