US President Barack Obama has defended an interim deal with Iran to curb its nuclear programme.

He has pledged to step up sanctions or prepare for a potential military strike if Tehran fails to abide by the pact.

US relations with Israel have been strained by the interim agreement, reached between Iran and major world powers including the US.

The deal designed to halt further advances in Iran's nuclear programme and buy time for negotiations on a final settlement.

The US said the agreement will give the international community time to see if Tehran is serious about curbing its nuclear ambitions.

It will also provide some relief from sanctions that have crippled its economy.

Israel believes any sanctions relief is a dangerous gift to a country that it says threatens its very existence.

Israeli Prime Minister Benjamin Netanyahu has called the deal reached in Geneva an "historic mistake".

Mr Obama said he viewed the likelihood of a satisfactory "end state" as a 50/50 proposition.

He repeated that all options remained on the table if Iran did not follow through with its obligations.

Mr Obama said it was unrealistic to believe that Iran would halt and dismantle its nuclear programme completely, if the successful sanctions regime were continually strengthened and talks were not given a chance to succeed.

Elsewhere, Afghan President Hamid Karzai agreed on a cooperation pact with Iran, while continuing to resist signing a long-term security agreement with the United States.

 Mr Karzai struck the deal with Iranian President Hassan Rouhaniin Tehran in a move that will be greeted with suspicion by his US ally.

The US is trying to convince him to sign the security accord governing any post-2014 US presence in Afghanistan.