US stock index futures moved lower after Washington turned down Iran's proposal, cooling market optimism over a near-term deal to reopen the Strait of Hormuz.

Futures on the S&P 500 and the Nasdaq 100 each fell 0.3%.

Reports say Iran is holding firm to its plan to reopen the strait within seven days and will not soften its own conditions, while US President Trump has sent mixed signals about his willingness to negotiate.