Ridding Syria of chemical weapons is consuming the time of international negotiators, but Iran's nuclear programme is where the focus inevitably has to turn. US President Barack Obama has shown his understanding by sending a letter to his Iranian counterpart, Hassan Rowhani, congratulating him for his election win and offering to help resolve the nuclear issue. Speculation is rife that they will meet on the sidelines of the UN General Assembly this week. The Iranian leader, unlike his stridently anti-Western predecessor, Mahmoud Ahmadinejad, has given a conciliatory response, offering hope of a solution, discussion of broader Middle East challenges and improvement of ties with the US. The diplomacy is at an infant stage, and has to be nurtured so that there is a chance of the region's problems being resolved.

Syria's civil war is a tragedy for its people and a challenge for neighbouring countries flooded by refugees. But while the international community can help destroy its chemical weapons and broker dialogue, the conflict is for Syrians to resolve. Iran is no such localised matter, though; the issues are of regional and global interest. Ensuring its nuclear programme is, as Rowhani says, for peaceful purposes, is essential if proliferators like North Korea are to be kept in check. Tehran has also helped destabilise the Middle East by threatening Israel and its ally, the US, supporting Muslim extremist and sectarian groups, and inspiring anti-West radicalism.

The US is well placed to take the initiative. Iran has been among its bitterest rivals since the Islamic revolution of 1980, when ties were severed. Rowhani's apparent willingness to address concerns since taking office in June and Obama's reaching out are the most positive developments for years.