“There will be more sanctions to come, and Iran’s economic problems and challenges are going to compound in 2020,” a senior State Department official told CNBC on Monday.

“They are already deep into a recession, and we are also seeing Iran come under greater diplomatic isolation,” the unnamed official was quoted by CNBC as saying.

According to another senior State Department official quoted by CNBC, the Trump administration has sanctioned approximately 1,000 individuals and entities with links to Iran's "malign activities".

“What we are doing is denying the regime the revenue that it needs to run an expansionist foreign policy, and by that policy, Iran has less money to spend today than it did almost three years ago when we came into office,” the official told CNBC.

On Monday the U.S. Special Representative for Iran, Brian Hook, also emphasized that the Trump administration will continue its maximum pressure campaign in 2020.

The U.S. Special Representative for Iran also said the Islamic Republic is facing the worst financial crisis and political unrest in its 40-year history and in 2020 will face an even more difficult period.

"What we saw was an erosion of deterrence of Iran for the many years preceding President's election three years ago," he said ​ and added that the Trump administration is trying to reverse the gains made by Iran over those years.

Referring to the U.S. strikes on Iran-backed militia in Iraq on Sunday which killed 25 fighters, Hook said "If we're attacked, then we're going to respond, as the President did yesterday".

In an interview with Alhurra television on Monday Hook also said that Washington would not tolerate Iranian lawlessness in the region and in Iraq and added that Iran doesn't care about Iraq's and wants to dominate it.

The American strikes came two days after a missile attack on an Iraqi base where American forces are present, and that led for the first time to the death of an American contractor in Iraq.