Washington: President Barack Obama secured a landmark foreign policy victory yesterday as US Senate Democrats amassed enough votes to ensure the Iran nuclear deal survives in Congress, despite ferocious opposition from Republicans and the government of Israel.

Democratic Senator Barbara Mikulski became the crucial 34th vote in favour of the agreement in the 100-member chamber. The backing from Mikulski gives supporters the margin they need to uphold an Obama veto of a congressional resolution of disapproval if Republicans pass such a measure later this month.

The agreement signed by Iran, the US and five other world powers limits Iran’s nuclear programme in exchange for hundreds of billions of dollars in relief from international sanctions. Republicans and Israeli officials contend that concessions made to Iran could enable the country to wreak havoc throughout the Middle East.

In a letter delivered to Congress yesterday, Secretary of State John Kerry called Israel’s security “sacrosanct,” recounting the billions of dollars the US has provided the Jewish state for missile defence and other security assistance.

The letter was sent as Kerry defended the Iran deal in Philadelphia. His speech was carried live on television in Iran, an unusual occurrence. In an impassioned address Kerry reiterated the arguments he has been making in the two months since the deal was signed, insisting it is not based on trusting Tehran but on its ability to police its activity.

“The United States and the international community will be monitoring Iran non-stop and you can bet that, if we see something, we will do something,” he said. “The agreement gives us a wide range of enforcement tools, and we will use them. And the standard we will apply can be summed up in two words: ‘Zero tolerance.’

“There is no way to guarantee that Iran will keep its word, and that’s why this isn’t based on a promise or trust, but we can guarantee that Iran will regret breaking any promise it has made.”