With a mere few weeks left to reach a final agreement, nuclear negotiations between the US and Iran are at a "difficult" point, said an official US source. "The next phase of this process will be difficult because we will be focusing on the details," a senior US official told reporters on Wednesday on condition of anonymity, according to the Wall Street Journal. "It doesn't help anyone to delay tough decisions as they become tougher over time," he added. Negotiators have been unable to reach a breakthrough and are likely to remain in Vienna till the end of this month. For the US, it will be "essential" and "crucial" that any pact with Iran must include a large monitoring of Iranian activities.