Iran’s chief nuclear negotiator and Parliament Speaker Mohammad Bagher Qalibaf Saturday warned that any fresh US military action against Tehran will be “more crushing and bitter for America than the first day of the war”, as Pakistan Army Chief Field Marshal Asim Munir held a packed day of talks in the Iranian capital aimed at reviving stalled US-Iran negotiations.Munir met Qalibaf, Iranian President Masoud Pezeshkian and Foreign Minister Abbas Araghchi during the visit, his second trip to Tehran in just over five weeks, Iranian state media and Pakistan’s Inter-Services Public Relations (ISPR) said.The visit comes nearly three months after the US and Israel launched joint strikes on Iran on February 28, and amid mounting fears that the Trump administration could resume military operations, with US officials reportedly preparing a fresh round of strikes.‘Military men know the value of peace’In remarks during his meeting with Munir, Qalibaf accused Washington of starting the war “while negotiations were underway” and now seeking talks to end it, a reference to the collapse of the April 8 Pakistan-brokered ceasefire and the US naval blockade that followed.“We were in a ceasefire that you brokered when the United States broke its word, imposed a naval blockade, and now it is looking to lift it,” Qalibaf was quoted as saying by Iran’s Mehr News Agency.He added, “Military men know the value of peace better than others, but they will never allow their country’s dignity and rights to be trampled.”Warning that Iran’s armed forces had used the truce period to rebuild, Qalibaf said, “If Trump acts foolishly and restarts the war, it will certainly be more crushing and bitter for America than the first day of the war.”Story continues below this adMunir’s responseMunir, according to the Iranian readout, struck a conciliatory tone, telling Qalibaf that “the government and people of Pakistan hold the best wishes and prayers for the future of the Iranians.”“You and I are both soldiers of our nations, and soldiers speak without stuttering and with honesty,” Munir was quoted as saying. He added that he was pleased Iran was being administered by “intelligent people with high vision at this juncture”.The Pakistan Army chief was received in Tehran by Iran’s Interior Minister Eskandar Momeni. Pakistan’s Interior Minister Mohsin Naqvi, who is believed to be close to Munir, was already in the Iranian capital and had been engaging top Iranian officials when the field marshal arrived, Pakistani military officials said.A second mediation trip in five weeksThis is Munir’s second visit to Tehran since the war began. He travelled to Iran for three days in mid-April alongside Naqvi, meeting Pezeshkian, Qalibaf, Araghchi and senior commander Major General Ali Abdollahi.Story continues below this adThat earlier visit set the stage for the Islamabad Talks of April 11-12, the first direct US-Iran negotiations since the 1979 Iranian Revolution, led on the US side by Vice President JD Vance. The talks failed to clinch a deal, with Iran’s nuclear programme and control over the Strait of Hormuz identified as key sticking points.US Secretary of State Marco Rubio said Friday that Pakistani mediators were doing an “admirable job,” telling reporters, “There’s been some progress. I wouldn’t exaggerate it, I wouldn’t diminish it. There’s more work to be done.”Rubio confirmed the US was in “constant communication” with Munir.The blockade and the broken ceasefireThe April 8 Pakistan-brokered ceasefire collapsed within days. On April 13, the US imposed a naval blockade on Iranian ports along the Persian Gulf and Strait of Hormuz, deploying over 100 military aircraft to patrol the waterway, according to US Joint Chiefs Chairman Gen. Dan Caine.Story continues below this adOn April 19, US forces seized the Iranian-flagged cargo ship Touska in the Gulf of Oman after it allegedly tried to evade the blockade. Iran’s joint military command called the boarding “an act of piracy” and reblockaded the strait in retaliation, with the Islamic Revolutionary Guard Corps (IRGC) announcing the closure of the waterway to US and Israeli-linked vessels.The Strait of Hormuz handles roughly one-fifth of the world’s daily energy supplies in normal times. Shipping disruptions have triggered energy shortages and stoked inflation across Asian and European economies, including India.Why Pakistan?Pakistan has emerged as the principal back-channel mediator in the conflict because it enjoys the confidence of both Tehran and Washington, a unique position in the current crisis.The role has elevated Munir’s diplomatic profile considerably. The Field Marshal, who was promoted to that rank after the May 2025 India-Pakistan standoff, now operates in close coordination with Pakistan Prime Minister Shehbaz Sharif on the Iran file.Story continues below this adAccording to security sources cited in Pakistani media, the Munir-Sharif team is now pushing for a second round of US-Iran direct talks to be held in Islamabad before any return to open hostilities.Trump weighs fresh strikesThe Tehran meetings come amid reports that President Donald Trump is preparing a fresh round of military strikes against Iran. Sources with direct knowledge of the planning told CBS News on Friday that no final decision had been taken, but several US military and intelligence officials had cancelled Memorial Day weekend plans in anticipation.Trump on Friday cancelled his trip to his New Jersey golf property and confirmed he would skip the wedding of his eldest son, Donald Trump Jr., to Bettina Anderson in the Bahamas, citing “circumstances pertaining to government.”“I feel it is important for me to remain in Washington, D.C., at the White House during this important period of time,” Trump wrote on Truth Social.(With inputs from agencies)