U.S. Secretary of State Marco Rubio voiced hope on Thursday of progress on ending the war with Iran, with mediator Pakistan's army chief due to arrive in the Islamic republic for talks.

The expected visit by Field Marshal Asim Munir, a powerful figure with a growing role in Pakistan's foreign relations, comes a day after U.S. President Donald Trump warned that negotiations to end the war were on the "borderline" between a deal and renewed strikes.