Last-Minute objections by five Shi’ite leaders forced the indefinite postponement of Friday’s signing of an interim Constitution for Iraq, threatening US plans to hand sovereignty back to Iraqis on June 30.Sources said the five dissenters were following the advice of Iraq’s most revered Shi’ite leader, Ayatollah Ali Al-Sistani, and were pushing for greater Shi’ite influence in a sovereign Iraq — which may put them on a collision course with Sunni Arabs and Kurds who also want their voices heard. It was the second delay in signing the document.One major point of contention was a clause on a referendum due to be held next year to approve a permanent Constitution once it has been drawn up. The clause states that even if a majority of Iraqis approves the Constitution, it can be vetoed if two-thirds of voters in three provinces reject it. ‘‘At the last minute, the very last minute, there was a switch by the Shi’ites and they objected strongly to a clause which says that if three provinces don’t agree on the Constitution then it goes back (to Parliament),’’ Mahmoud Othman, a Kurdish member of the Council, said.‘‘They consider that a provocation and the imposition of the will of the minority on the majority.’’ —(Reuters)