BAGHDAD - Iran's insistence that world powers acknowledge what it sees as its right to enrich uranium emerged as a significant difference in international talks on its nuclear energy program this week, a senior US administration official said.Speaking after two days of discussions between Iran and six world powers aimed at trying to defuse fears of a covert Iranian effort to develop nuclear bombs, the official added that looming additional sanctions were likely to raise pressure on Iran to seek an agreement ahead of a further round of talks in mid-June. "These were difficult talks ... obviously we were far apart (at the start)," said the official, who declined to be identified due to the sensitivity of the subject.The official said a "significant difference" at the meeting was Iran's insistence that its right to enrich be recognized."Obviously (that) was not something we were prepared to do," the official said, echoing the US view that Iran does not automatically have this right under international law because, it argues, Iran is in violation of its obligations under counter-proliferation safeguards.Work would continue at the next round of talks, set for Moscow on June 18-19, towards a deal for a suspension of enrichment of uranium to a fissile purity of 20 percent, the official said.That is the nuclear advance most worrying to the West since it clears technical obstacles to reaching 90 percent, or bomb-grade, enrichment. Iran says it will not exceed 20 percent and the material will be made into fuel for a research reactor."We never expected to get that agreement (on 20 percent) here in Baghdad," the official said."There is agreement to address all aspects of 20 percent as we put it on the table."The official said the six powers were going to try to advance the talks "as fast as we can." But it was too early to talk about technical level or expert meetings because the political issues still needed to be clarified.The official said sanctions coming into effect in coming weeks would increase leverage on Iran in the negotiations."Maximum pressure is not yet being felt by Iran," the official said, adding there were many other potential sanctions that remained to be employed.Tehran wants any nuclear deal to spare it from an EU embargo on its oil exports to be phased in fully by July 1. It also wants an end to trade and diplomatic sanctions imposed since 2006.