US Secretary of State Marco Rubio voiced hope of progress on ending the war with Iran, as he looked to Pakistani mediators to help advance efforts to strike an agreement. Previous comments by President Donald Trump had suggested weeks of stop-start negotiations to strike a permanent end to the war were teetering on the "borderline" between a deal and renewed attacks."I believe the Pakistanis will be travelling to Tehran today. So hopefully that'll advance this further," Rubio told reporters on Thursday.A ceasefire on April 8 halted the war launched weeks earlier by the United States and Israel, but negotiation efforts, including historic face to face talks hosted in Islamabad have so far failed to yield a lasting agreement.Pakistan's interior minister Mohsin Naqvi, who is widely considered close to Pakistan's powerful army chief Asim Munir, visited Iran for the second time in a week on Wednesday. Iranian media, including the ISNA news agency, had reported based on unnamed sources that Munir could himself visit Tehran as early as Thursday, but there was no comment from Pakistan authorities about any travel plan for the army chief.Beijing did however, announce that Pakistan Prime Minister Shehbaz Sharif will travel on Saturday to China, which has also been involved in mediation efforts to end the war.- 'Borderline' -Though open warfare and strikes across the Gulf have reduced, the impasse continues to weigh on the world economy.In April, Pakistan hosted the only direct negotiations, which Munir helped mediate, between US and Iranian officials to take place since February 28, when the war began.But the talks ultimately failed, with Tehran accusing Washington of making "excessive demands".