Israel is concerned that the increased coordination between the US and Iran over fighting Isis could lead to a weakening of the American stance in talks over the Iranian nuclear programme.
A high-level Israeli delegation was in Washington this week for the annual strategic dialogue between the two countries. Among the items on the agenda was the next round of P5+1 talks to take place later this month on the sidelines of the UN General Assembly in New York.
The talks were supposed to have delivered a comprehensive agreement on Iran's nuclear programme by the end of June. The negotiations stalled, however, over the Iranians' insistence on retaining a significant uranium enrichment capability, and a new deadline has been set for November.
Strategic Affairs Minister Yuval Steinitz led the delegation to Washington. It included senior representatives of the IDF, the Foreign Ministry, Mossad and Israel's Atomic Energy Committee.
According to Israeli officials, the main concern was to ensure that the US is not planning to make any concessions to the Iranians in the P5+1 talks.
The concerns have grown alongside reports of growing secret co-operation between the US and Iran as part of the ongoing air campaign against Isis targets.
The Israeli delegation was due to present US officials with intelligence assessments showing that Iran has no plans to seriously curb its nuclear weapon capabilities, even if it may delay these in the hope of reducing international sanctions. Israeli officials were disappointed that the P5+1 nations group decided to have Catherine Ashton continue leading the negotiations despite her stepping down next month as EU foreign policy chief. Baroness Ashton is seen by many Israeli observers as having been "over-friendly" towards the Iranians.
Meanwhile, the International Atomic Energy Agency (IAEA) announced on Friday that Iran had failed to meet a deadline at the end of August for providing new information on its nuclear programme. According to a deal signed by Iran and the IAEA last November, Tehran was to have handed over information on 13 areas of concern over its nuclear programme. So far, the Iranians have complied in only one of those areas. A US State Department spokeswoman said that progress on the deal was "a key part" of the talks "and it's something we are very concerned about."