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Barack Obama, the US President, has promised tougher sanctions against Iran over an alleged plot to kill the Saudi ambassador to Washington.

But some are questioning whether further measures against Tehran will be effective.

The Iranian Republic is already weighed down with economic penalties, some dating back for more than 30 years, which have so far failed to alter the country's political course.

Al Jazeera's Kimberly Halkett reports from Washington.

Source: Al Jazeera