While the Obama administration is trying to convince the Israeli government to give diplomacy and sanctions against Iran a chance before launching a military strike, senior American officials said this week that the US will supply Israel with new bunker-busting bombs and aerial tankers.

The Israeli media made much of these promises, also because it was one of the few concrete achievements of Benjamin Netanyahu's visit to Washington, but the weapon systems will have little effect on Israel's capability to attack Iran's nuclear installations.

Israel ordered a hundred 5,000lb GBU-28 bombs, which are capable of penetrating about 100ft of earth or 20ft feet of concrete. It is one of the most powerful bunker-busting missiles in the American arsenal and, according to various reports, 55 units have been delivered so far.

A larger number of bombs will naturally give the Israeli air force more flexibility in planning and executing a complex attack on the Iranian nuclear programme, since many of the key sites are fortified or underground.

The same is true of additional aerial tankers. These petrol-stations in the sky allow Israel's combat jets to fly farther, giving give them more "loiter"time over a target area. But Israel already has nine converted Boeing 707s and additional tankers - while making the IAF planners' lives easier - won't fundamentally change the nature of the mission.

"More bunker-busters and tankers will be helpful," says one Israeli security source, "but it doesn't change the picture as we already believe we can do the job with what we have now. I think this is mainly the US trying to make us and the pro-Israel lobby feel better while they continue with diplomacy. As it is, these bombs and tankers are not there on the shelf, it will take months for them to reach Israel so we may not even have them for an attack this year."