TEHRAN, Iran — Senior Iranian lawmakers rejected on Saturday a U.N.-backed plan to ship much of the country’s uranium abroad for further enrichment, raising further doubts about the likelihood Tehran will finally approve the deal.

The UN-brokered plan requires Iran to send 1.2 tons of low-enriched uranium — around 70 percent of its stockpile — to Russia in one batch by the end of the year, easing concerns the material would be used for a bomb.