Iran's chief negotiator warned the United States is not to be trusted Sunday, saying Tehran would not agree to any deal with Washington unless it fully secures Iranian rights.Mohammad Bagher Ghalibaf's remarks came as reports emerged that US President Donald Trump had sent a tougher peace proposal back to Iran, and underlined the rift that the parties still need to close.Any further tweaks to the draft could further delay an agreement to formally end the Middle East war and reopen the Strait of Hormuz after weeks of fraught negotiations marked by sharp rhetoric and occasional flare-ups of violence.Iran was already in negotiations with the United States about the fate of its nuclear programme in February, when the US and Israel launched air and missile strikes that wiped out much of the Islamic republic's senior leadership.And, while Tehran has long insisted that its nuclear programme is for purely civilian ends, the United States and its Western allies have long suspected it aims to develop a weapon.- Nuclear guarantees -The New York Times and Axios reported on Saturday that Trump had sent back a "tougher" new framework to be considered by Iran, though details remain unclear.Trump has said his priorities include stopping Iran from any nuclear weapon development and re-opening the Hormuz shipping lane, over which Iarn has sought to impose control since the war began.