Barack Obama yesterday coupled a pledge that he was prepared to use military action if necessary to prevent Iran from acquiring nuclear weapons with a clear warning that "too much loose talk of war" had actually been helpful to Tehran.

On the eve of a crucial meeting today with the Israeli Prime Minister, Benjamin Netanyahu, the US President repeatedly emphasised his preference for a diplomatic solution, backed by sanctions. "For the sake of Israel's security, America's security and the peace and security of the world, now is not the time for bluster. Now is the time to let our increased pressure sink in, and to sustain the broad international coalition that we have built," he said in a speech to a conference organised by the American Israel Public Affairs Committee (Aipac) in Washington DC.

In doing so, and while forcefully warning that a nuclear-armed Iran ran completely counter to both Israel's and the US's security interests, Mr Obama did little to gloss over the issues at the heart of a disagreement between the US and Israel over their strategy towards Tehran's nuclear programme. Key to these differences are two closely-linked issues of timing. For Israel, the "red line" comes when Iran is capable of building a nuclear weapon. According to most Israeli readings, Iran is – thanks to its enrichment of uranium – not far off that point.

For the US administration, the red line comes significantly later, namely if and when Iran starts building, or at least decides to build, a nuclear weapon. This is why President Obama chose his words carefully when he spoke yesterday of his determination to prevent Iran from "acquiring a nuclear weapon", and this why he believes there is time for sanctions and diplomatic pressure. He will tell Mr Netanyahu that these offer a more "permanent" means of solving the problem than a bombing strike that would only set back a military nuclear programme for a few years at most, and might actually strengthen the Iranians' resolve to press ahead with it.