The prospect of a successful conclusion to the talks on Iran's nuclear programme that start in Kazakhstan tomorrow was never high. Despite tentatively positive noises from both Tehran and Washington in recent months, decades of stalemate can hardly inspire optimism. And the latest developments leave the likelihood of a deal slimmer than ever.

Last week, the UN nuclear watchdog confirmed that Iran was going ahead with plans to install next-generation centrifuges at its plant at Natanz. The new equipment can enrich uranium at two or three times the rate of that it replaces, raising Western fears of an escalation of the weapons programme that Tehran consistently denies. Even if – and it is a big if – Iran is not trying to build a weapon now, faster centrifuges could give it the ability to make a sudden "dash" for a bomb.

Then, last weekend, the Iran Atomic Energy Organisation announced the discovery of sufficient raw uranium deposits to treble the country's stock. It also claimed to have identified 16 more sites for the civil nuclear power stations that Tehran claims to be the ultimate destination for its nuclear fuel.

Neither move inspires confidence ahead of this week's talks. And when the so-called P5+1 group – Russia, China, Britain, France, Germany and the US – meet in Almaty both issues will be high on the agenda. There is no option but to press ahead as planned, however. And that means offering Iran more tempting incentives to scale back its enrichment programme.

It is not entirely unrealistic to hope Tehran might show some willingness to negotiate in return. For all the recent posturing, sanctions are biting too hard to be tolerated indefinitely. It is as well to be realistic, though. Ayatollah Ali Khamenei has little room to manoeuvre ahead of the presidential elections in June.

There is still time for diplomatic bridge-building. Even with the new kit, Iran's bomb-making capability is not yet beyond control. Israel has backed off, at least in the immediate term. But the game of cat-and-mouse that has gone on for so long cannot go on forever.