Iranian officials said Monday that within weeks they could exceed an internationally agreed cap on their stockpile of low-enriched uranium, as tensions between Iran and the U.S. escalated. Iran threatened earlier this month to step up its nuclear program, saying it would initially stop respecting limits set on its stockpiles of enriched uranium and heavy water, both of which can be used in the production of nuclear weapons. Tehran warned that without economic help from Europe to buffer the effect of renewed U.S. sanctions,…