For many experts, US President Donald Trump's "Muslim ban" is not only unconstitutional and dangerously divisive, it also contradicts what the new US leader claims he aims to achieve through this move - stopping terrorist attacks perpetrated by foreigners on US soil.

Trump's ban targets seven predominantly Muslim countries - Syria, Iran, Iraq, Sudan, Libya, Somalia and Yemen - whose citizens have so far not been involved in mass killings in the US. On the contrary, all major terrorist groups that have attacked the United States and other Western countries over the past couple of decades - from al Qaeda to the Taliban to the so-called "Islamic State" (IS) - can trace their roots back to Sunni-led countries, particularly Saudi Arabia, Pakistan and Qatar. But conspicuously these countries didn't make the list.

Not only that, in a telephone call on Sunday with Saudi Arabia's King Salman, Trump reiterated his administration's support to Riyadh. A White House statement said the two leaders discussed Trump's role "to lead a Middle East effort to defeat terrorism and to help build a new future, economically and socially," for Saudi Arabia and the region.

In an interview with DW, US-based security and Islamism expert Arif Jamal says while it is too early to evaluate President Trump's decisions, it is clear that the US cannot win the war against radical Islam as long as Saudi Arabia and Pakistan are its allies.

DW: While Saudi nationals were involved in the September 11, 2001 terrorist attacks, the recent killings on US soil - the Orlando and San Bernardino shootings - were perpetrated by people of Afghan and Pakistani origin. Why did President Trump exempt these countries from the executive order?

Arif Jamal: It is too early and very difficult to evaluate President Trump's strategy. Although the US media is claiming that Trump spared these countries because he has business ties with them, this may only be true for Saudi Arabia. He has no investments in Pakistan and Afghanistan.

I believe he didn't put Afghanistan on the list because it would have created a lot of problems for US troops and other Americans working in the war-torn country. It is obvious that the Afghan government would have stopped cooperating with Washington if he had made such a move. Pakistan's case is different, and I think Trump is in the process of formulating a comprehensive policy for the Islamic country.

Arif Jamal is a US-based journalist and Islamism expert

But one thing is pretty clear. The US cannot win the war against Islamism as long as Saudi Arabia and Pakistan are its allies.

It seems the new US president's geopolitical alliances in the Middle East and South Asia are not much different from his predecessors, Barack Obama and George W. Bush. Do you agree with this assessment?

Again, I think it is too early to make this judgment. Trump is definitely revisiting the Obama administration's policy on Iran. On the other hand, in the current situation, Iraq can hardly be called a US ally.

However, reports suggest that President Trump is seeking Russia's help to coordinate policies against the IS terror outfit. If that becomes reality, it would be a whole new game. But it would be very difficult for Trump to be too close to Moscow as there is strong opposition against such a move in the US. But in my view, it is impossible to defeat radical Islam without Russia's help.

Why is Trump reluctant to be tough on Pakistan and Saudi Arabia? What makes the US relations with Islamabad and Riyadh special?

I think President Trump will be tougher on Pakistan in the coming weeks and months. However, the same cannot be said about Saudi Arabia. But I would reiterate that Washington cannot defeat radical Islam and jihadist groups if it refuses to take strong actions against Saudi Arabia.

Will Pakistan and Saudi Arabia be now emboldened in their alleged support for radical Islamists knowing that Trump has excluded them from a direct ban?

Neither Pakistan nor Saudi Arabia see an ally in Trump. In fact, no Muslim-majority country is friendly towards him. This is the reason why Muslims from all over the world are taking part in anti-Trump demonstrations. These are the same Muslims who hardly take to the streets to protest against Islamists or their own governments.

How will Trump's obvious anti-Iran stance impact the Sunni-Shiite sectarian strife in the Middle East and Pakistan?

If Washington and Moscow forge an alliance in the battle against IS, Trump will have to soften his position on Iran. It will also help reduce sectarian tensions in the Middle East and South Asia. But the visa ban on seven Muslim-majority countries shouldn't be seen as a comprehensive policy on the Muslim world. So far, Trump has only acted to unite his supporters - white supremacists and Christian fundamentalists. We shouldn't read more into it.

Arif Jamal is a US-based journalist and author of several books, including 'Call For Transnational Jihad: Lashkar-e-Taiba, 1985-2014.'

The interview was conducted by Shamil Shams.