WASHINGTON – The United States wants to send robotic explorers to the moon as soon as next year as a preparatory step towards sending astronauts back there for the first time since 1972, a Nasa official said on Monday.

The National Aeronautics and Space Administration (Nasa) is planning a series of lunar missions beginning next year aimed at developing the capacity for a return to the moon, said Cheryl Warner, a spokeswoman for Nasa&39;s Human Exploration Directorate.

Nasa will work with private companies, which have not yet been chosen, on the missions, Warner said in a phone interview.

US President Donald Trump in December signed a directive that he said would enable astronauts to return to the moon and eventually lead a mission to Mars. Last month, he ordered the government to review regulations on commercial space flights.

Trump is due to meet with his National Space Council on Monday.

Americans first landed on the moon in 1969, reaching a goal set by former President John F Kennedy in 1961 and capping a decade-long space race between Washington and Moscow.

Since then, US efforts to explore beyond the Earth&39;s orbit have largely focused on remote spacecraft that do not have human crew members, though American presidents have repeatedly raised the idea of sending human explorers back to the moon or further.

President George W Bush in 2004 said humans would return to the moon by 2020. His successor, President Barack Obama, said in 2016 the United States would send humans to Mars by the 2030s.