A senior UN official says Israel is now left without an excuse to evade ratifying the Comprehensive Nuclear Test Ban Treaty (CTBT) after a nuclear deal between Iran and the West.

Lassina Zerbo, the executive secretary of the CTBT Organization, said with the implementation of the nuclear deal, Israel’s biggest pretext for refraining from ratifying the CTBT has been taken away.

He made the remarks to a week-long conference marking the 20th anniversary of the treaty being opened for signing in the Austrian capital, Vienna.

The Comprehensive Nuclear Test Ban Treaty has 196 members but the treaty has not entered into force because it still needs ratification by nuclear-armed signatories such as the US, China, Israel, India, Pakistan and North Korea.

Zerbo said Israel is "the closest" of the signatories to ratifying the treaty and assuring the world it will never conduct a nuclear test explosion.

That is because "the biggest threat for Israel is gone and over" after Iran reached a nuclear agreement with the US, Britain, France, China, Russia and Germany in July, he said.

An open secret for decades, the Israeli atomic stockpile is estimated at some 200-400 warheads, though Israel refuses to confirm or deny its existence under a policy of deliberate ambiguity.

Israel is also refusing to sign the nuclear Non-Proliferation Treaty (NPT) and denying international access to its atomic arsenal.

Zerbo said he is hoping to visit Israel and talk to its leaders although he doesn't expect immediate results on ratification.

"I think that they're the ones who can unlock what is stopping the CTBT from moving," he said.

Zerbo is also hoping to visit Iran, which signed CTBT in 1996, to convince the country to ratify the treaty.

The Islamic Republic says its nuclear program is aimed at generating electricity. The country is an NPT signatory and its nuclear facilities are open to regular UN inspections which have not found any diversion.

Zerbo, however, said if both Iran and Israel signed CTBT, it would "provide momentum — first for Egypt to ratify the CTBT and then to start negotiations for a nuclear test-free zone in the Middle East."

"You can't jump and get a weapon-free zone in the Middle East if the CTBT isn't ratified," he said.

Israel's arsenal is the only obstacle to a Middle East free of nuclear weapons because no country possesses a nuclear arsenal in the region other than the Tel Aviv regime.

Zerbo also said China won’t ratify the CTBT before the US, India won’t ratify before China, and Pakistan won’t ratify before India. He also emphasized that US action is crucial in this regard.

He said North Korea is the least likely country to ratify the CTBT.

The UN official said the international community needs to change the way it engages with North Korea.

“What they need at this point in time is... maybe a bit of respect and dignity in the dialogue we have with them.”

By Press TV