Iran has submitted a nuclear proposal to the United States through Qatar but insists that Washington meet seven demands before negotiations can begin, as fresh attacks on shipping, missile interceptions and a crackdown on clerics in Bahrain underscored mounting tensions across the Gulf. A senior Iranian official told Reuters on Thursday that Washington was reviewing the proposal, which would only be discussed after the United States addressed Tehran's conditions. Iran's demands include lifting US sanctions, releasing frozen Iranian assets and paying war reparations. Iran's deputy security chief Ali Bagheri Kani said that Tehran was not satisfied with "paper commitments" and wanted practical American steps before any new diplomatic engagement. Senior security official Mohsen Rezaei had also warned that Iran would neither reopen the Strait of Hormuz nor negotiate without its seven conditions. Meanwhile, a seafarer was killed in an explosion believed to have resulted from a missile attack on an oil products tanker in the Gulf on Thursday. The Marshall Islands-flagged MT Velos Sapphire was sailing towards Bahrain when it was struck. Its remaining crew extinguished a fire, while the vessel was taken to Bahrain's Khalifa Bin Salman Port for investigation. Separately, the UK Maritime Trade Operations agency said a tanker reported an explosion near its port-side waterline while crossing the Strait of Hormuz, 16 nautical miles east of Oman's Khasab. The vessel remained operational and all crew members were safe. In Bahrain, authorities have intensified a crackdown on clerics accused of promoting allegiance to Iran. More than 50 clerics and religious figures were arrested between May and June over alleged efforts to incite rebellion and overthrow the government with Iranian backing. Bahrain's security chief Tariq Al Hassan said the authorities were confronting an ideology that placed obedience to Iran's leadership above national sovereignty. However, lawyers and relatives of the detained clerics denied the allegations. Elsewhere, Saudi-led coalition air defences intercepted two ballistic missiles fired by Yemen's Houthi group towards Najran on Friday. Meanwhile, the Houthis said 30 people were killed and eight injured in a separate strike on a market in Yemen's Taiz province, blaming Saudi aircraft for the attack.