The US National Highway Traffic Safety Administration (NHTSA) has sent Tesla Motors a detailed list of questions regarding its Autopilot feature and a 7 May fatal crash in Florida in which the system was in use, it was reported on Tuesday.

According to Reuters, the nine-page letter dated 8 July was made public today and requires the automaker to file responses in the coming weeks. The letter is a standard part of a formal defect investigation by the auto safety agency. Some answers are due by 29 July and others by 26 August, NHTSA said.

The letter sought details of all design changes and updates to Autopilot since it went into use last year - and whether Tesla plans any updates to the system in the next four months.

It also sought records and data logs of all crashes that could be linked to the software and the version of Autopilot in use of the time.

The letter disclosed that Tesla and NHTSA officials met on 14 June - two weeks before the agency opened a formal investigation.

NHTSA spokesman Bryan Thomas told Reuters the agency "has not made any determination about the presence or absence of a defect in the subject vehicles".

Tesla didn't immediately respond to a request for comment.

Separately, the US Securities and Exchange Commission is investigating whether Tesla waited too long to disclose a fatal crash in May that called into question the safety of the Autopilot system in the car that takes control of steering and braking, the Wall Street Journal reported on Monday, citing an unnamed source.

The National Transportation Safety Board is sending a five-person team to Florida later this week to investigate that crash, said Christopher O'Neil, a spokesman for the agency, which makes recommendations to regulators and companies about transportation-related safety issues.