ISLAMABAD, April 22 -- Last-minute ceasefire talks between the United States and Iran looked uncertain Tuesday as a two-week truce was set to expire and both countries warned that, without a deal, they were prepared to resume fighting. US Vice President JD Vance, expected to lead US negotiators if talks continue, called off a trip to Pakistan, a US official said. And Iran said it hadn't decided whether to participate. Pakistani leaders, including Prime Minister Shehbaz Sharif, worked intensively late Tuesday to get both sides to agree to a second round of ceasefire talks, according to two officials who spoke on condition of anonymity because they were not authorized to speak to the media. The ceasefire was set to expire Wednesday. Iranian F...