Iran has refused to answer International Atomic Energy Agency (IAEA) questions regarding its nuclear stockpiles for the first time since IAEA oversight went into effect in the country in 2016, according to The Wall Street Journal.

According to unnamed diplomats quoted in the report, Iran has not responded to requests for clarification regarding the alleged rebuilding of a dismantled site in Tehran which Israeli Prime Minister Benjamin Netanyahu has claimed is being used to resume nuclear activity using materials Iran had previously developed.

Netanyahu first raised the allegations in April 2018 in a dramatic, televised reveal of a huge collection of secret documents smuggled out of Tehran by Israel’s Mossad intelligence agency, which purported to detail Iran’s military nuclear program.

The documents detailed a secret Iranian nuclear program called Project Amad that ran from 1999 to 2003, the goal of which was to create five 10-kiloton-yield warheads for integration into a ballistic missile. Iran denied the existence of such a program when it agreed to the 2015 Joint Comprehensive Plan of Action (JCPOA), aka the “Iran nuclear deal.”

News of Iran’s noncompliance with the IAEA casts further doubts on the future of the JCPOA, from which the United States withdrew in 2018.