The US ambassador to the United Nations on Tuesday rejected suggestions by a UN panel that Washington has kept silent about Iranian sanctions violations in order to avoid disrupting fragile negotiations on a nuclear deal with Tehran.The UN Security Council's Panel of Experts on Iran said in April that it has received no new confirmed reports of Iranian violations despite several media reports of Iranian weapons shipments to Syria, Lebanon, Iraq, Yemen and Hezbollah and Hamas militants in violation of a UN embargo.US Ambassador Samantha Power was asked during a congressional hearing in Washington whether the administration of President Barack Obama has deliberately withheld reports of Iranian violations from the UN panel, which monitors UN sanctions violations."Absolutely not," Power said. "And I myself am often involved in raising sanctions violations that Iran has carried out. We have also, even over the life of this last delicate phase of negotiations, instituted more sanctions designations under the existing bilateral sanctions framework.""There's no pulling of our punches, even during these negotiations or ever," she said.