Iran's top diplomat is be the first state party to the 1970 nuclear Non-Proliferation Treaty (NPT) to address its 190 signatories at the United Nations headquarters in New York on behalf of 118 non-aligned nations that have signed the NPT, the world's benchmark disarmament pact.
Zarif and Kerry were to meet on the sidelines to discuss negotiations on a landmark nuclear deal with the United States and five other global powers as they try to secure a final agreement with Iran by a June 30 deadline.
"Beside taking part in the conference, we have come here to listen to Americans' explanations on the U.S. administration's undertakings and its domestic policies," Zarif told Iranian state television.
"We consider the U.S. government responsible for fulfilling its international commitments and under international laws," he said. "No government can evade such commitments because of its domestic issues."
Zarif appeared to be referring to U.S. Republican senators' pledge to try to toughen a bill giving Congress the power to review a nuclear agreement with Iran, a move that could further complicate the talks.
In a tentative deal reached on April 2 in Lausanne, Switzerland, between Iran and the six powers, Tehran agreed to curb sensitive nuclear work in return for ending sanctions.
Diplomats need to iron out details about the timing of sanctions relief, the future of Iran's atomic research and development program, the exact nature of the IAEA's monitoring regime, and what kind of uranium stockpiles Tehran will be allowed to keep under any final accord.
Sanctions are proving to be a key hurdle. Leader of the Islamic Revolution Ayatollah Seyyed Ali Khamenei has said all sanctions, including the most severe restrictions on its energy and financial sectors, should be lifted the moment a deal is signed.  
Western officials say that means sanctions will be lifted only after the IAEA verifies compliance.
Zarif again referred to sanctions in remarks to Iranian television.
"We have always said that sanctions and an agreement cannot go together and the other party should choose one of them," he said.
A senior Iranian negotiator said last week the latest round of nuclear talks in Vienna between Iran and the six powers had made good progress.
During this month's NPT meeting, Austria is leading an initiative to ban nuclear weapons due to the immense humanitarian suffering they cause. Over 70 countries are backing it 70 years after two atomic bombs were dropped on Japan.
The occupying regime of Israel, which opposes the nuclear deal with Iran, will be attending the conference as an observer for the first time since 1995.
The Zionist regime is widely believed to have the Middle East's only nuclear arsenal. Like nuclear-armed India and Pakistan, Israel is not a signatory to the NPT.  
The Israeli regime is widely believed to be the sole possessor of a nuclear arsenal in the Middle East with up to 400 undeclared nuclear warheads. Tel Aviv has rejected global calls to join the NPT and does not allow international bodies to inspect its controversial nuclear program.
"Unfortunately, Israel’s possession of nuclear weapons and its refusal to engage with the international community has become the greatest impediment to the universality of this treaty,” Zarif told Press TV.