A US official says a third American aircraft carrier is being sent toward Iran as Washington builds up its forces in the Middle East.

The official said the USS Theodore Roosevelt carrier strike group departed San Diego on Sunday, with the Makin Island Marine force following the next day. More than 2,000 Marines are aboard that force. The official expects three carriers and two amphibious landing groups near Iran by the end of November.

The deployment would add to a US presence of roughly 50,000 service members in the region. It comes amid both military pressure and diplomatic efforts involving Tehran.

Iran has put forward a seven-day proposal through Qatar: it would open the Strait of Hormuz again and return to nuclear negotiations if the US ended its naval blockade, eased sanctions and agreed to a regional ceasefire covering Lebanon and Yemen. US Ambassador to the UN Mike Waltz has said the demands involving frozen funds and sanctions relief are non-negotiable.