Jewish leaders do not come more much more influential than Daniel Mariaschin. As executive vice president of B'nai B'rith International and the director of the BBI Centre for Human Rights and Public Policy, the American has the ear of world leaders on matters of Jewish interest and much more.

B'nai B'rith has been accredited as a non-governmental organisation (NGO) by the United Nations since 1947 and as such plays a prominent role in campaigning and lobbying. So what does Mariaschin (pictured) plan to discuss with Foreign Office representatives - his next appointment after our interview?

Over coffee in a London hotel, to an incongruous jazz accompaniment, he does not need to ponder the question for long. The answer is Iran. It is his most pressing concern. "Iran is issue number one, issue number two and issue number three in importance. This is the kind of thing that NGO advocacy is all about. It is being the constant voice of warning, of caution."

So how worried do we need to be about Iran? "Very," he replies. "We have been saying for years that Iran is not just Israel's problem, and fortunately the democracies seem to be waking up to this now. We hope it's not too late. We hope that the current round of sanctions are going to have some impact."

If Iran remains unhindered, Mariaschin feels that, fairly soon, the country could have an operational nuclear missile pointing at Israel - and other countries too. "We are watching as Iran builds a complex deployment system for their warheads. We are not talking about crude devices but sophisticated weaponry. Their idea is to create inter-continental ballistic missiles," he says.

We need to be very worried. We hope it's not too late

However, he does not yet feel the time is right for military action. And if it becomes necessary he does not think it should be left to Israel alone. "We should not need to talk about this until every other possibility has been exhausted, and I don't think we have yet. We are only going to know if sanctions are effective if they have been applied as they are meant to be. We are going to have to cut off all the financial channels that allow the Iranians to move their money. It will only work if the front companies operated by the Iranian Revolutionary guard are shut down."

However, as befits a humans rights organisation, Mariaschin is not merely uncomfortable with Tehran's missile programme. "We also talk about the massive human rights abuses which have more or less escaped the attentions of the international community. We campaign over the treatment of women in Iran, the position of the minority Bahai faith. Iran is also the world's biggest abuser of the human rights of juvenile offenders."

B'nai B'rith has a particular focus on issues relating to Israel and world Jewry, although this does not stop the organisation taking a position over Darfur and other issues around the world.

Mariaschin, on a flying visit to Britain en route for Israel, is outraged that while Israel is constantly being called to account by human rights watchdogs, Iran can more or less do what it likes. "Has Amnesty International ever called upon Iran to stop arming Hizbollah and Hamas? Have there been special sessions at the United Nations called to condemn the firing of rockets into Israel?"

One of B'nai B'rith's other major spheres of interest is on worldwide antisemitism. But even here, Iran is involved, says Mariaschin. "Antisemitism masked as legitimate criticism of Israel has become mainstream and the Iranians have played a role in this." Unlike previously, he maintains, this hatred is no longer confined to the margins of society. "It could be church groups like the Presbyterians in the US, it could be over issues like universal jurisdiction. Then there is activity on the campuses, which is widespread in my country, and there are calls for cultural boycotts of Israel.

"The allegations of Israeli human rights abuses are coming from the centre now, and that is very concerning. It is here that NGOs like B'nai B'rith have a role to play. For example, we highlight editorial cartoons which depict Israelis as Nazis, make allusions to apartheid and make Israel into a pariah. Where do you draw the line? Believe me, you know antisemitism when you see it. You can tell when something is gratuitous."

Mariaschin was press secretary to former US Secretary of State Alexander Haig during his unsuccessful bid for the presidential in 1988, and joined B'nai B'rith at the conclusion of the campaign. In total, he has spent 37 years working for Jewish organisations. He sees his ability to lobby on Jewish issues as a privilege. "We work on Holocaust restitution, we engage on the peace process and on Iran. We are blessed to be living in a post 1948 world. But the question is what do we do with it? It is up to us to ensure the continued existence of a viable state of Israel in a world without antisemitism. And being able to make those cases gives me great comfort."