DW: The attacks on Iran's parliament and Ayatollah Khomeini's mausoleum have been claimed by Islamic State (IS) - a Wahhabi-Sunni militant group. The attackers, however, were Iranian nationals, as claimed by officials in Tehran. Does it show that IS influence is increasing in the Shiite-majority Iran?

Paulo Casaca: Iran has a long tradition of supporting terrorist groups not necessarily aligned with the Shiite sect of Islam, for instance al Qaeda, Hamas or the Taliban. Still, as it happens with other states that support jihadi groups, Iran cannot stop its own creations from turning against it. Pakistan is a good example in this case.

The non-Shiite jihadi groups have already increased their activities in Iran, particularly in its Sistan-Baluchestan province. IS had repeatedly announced its intentions to start operations in Iran, and now we saw the group attacking two important sites in the country.

Read: Iranian nationals committed twin attacks in Tehran, says senior official

Iranian authorities have condemned the Wednesday assaults, but it appears from their statements they are also downplaying the severity of the incident. Should Iranians be alarmed that such an attack could be perpetrated on its soil by an organization that is extremely anti-Shiite?

The Iranian propaganda machinery is pretty active in the wake of the attacks. The authorities are trying to confuse the situation. They want to make sure the Iranians don't get alarmed by the state support for terrorism but rather that people look at them as the ones who are opposing terrorist activities.

Iran rejected US President Donald Trump's statement on the attack as "repugnant" as he once again blamed Tehran for supporting terror outfits in the region. How valid is Trump's criticism of Iran and its alleged support for militant groups in the Middle East?

Donald Trump is the first US president since - and including - Jimmy Carter who has the courage to break with the policy of appeasement toward Tehran. Iranian authorities are very concerned by the formation of an anti-jihadi alliance in the Middle East. They have engaged in an active diplomacy against this alliance in countries like Qatar and Turkey. Regardless of the operational details of the IS attack, it is clear that Tehran is involved in a major propaganda campaign to spread confusion and portray itself as a victim of terrorism.

- Saudi Arabia vs. Qatar vs. Iran

- Pakistan on collision course with Iran?

Do the attacks prove that the region is entering a new era of proxy jihadism on the lines of Saudi-Iranian rivalry?

In the past few years, IS has perpetrated a number of terrorist attacks in Saudi Arabia. Riyadh has been engaged in a proxy war with Tehran long before Iran's Islamic revolution in 1979. The recent anti-terrorism summit in Riyadh seems to confirm that the Saudi establishment understands it has lost to Iran in this proxy war. I don't think that Riyadh wants to compete with Iran in this "game" any longer.

Saudi Arabia's reformation is, however, a long and difficult process, and its success is far from guaranteed. But the reports claiming that an alliance of Saudi Arabia, the US and Israel could be linked with the attacks on Iranian parliament and Khomeini's tomb cannot be taken seriously.

Can IS recruit fighters from Iraq, Pakistan and Afghanistan to perpetrate more attacks in Iran?

I think there are enough potential recruits in Iran that this will not be necessary. On the contrary, the Iranian recruitment of Shiite jihadis from countries like Iraq, Pakistan and Afghanistan has been crucial in its war efforts in Syria.

In the early 20th century, the ties between Shiite and Sunni jihadis were very close. Abul Ala Maududi had met with the architect of Iranian revolution, Ayatollah Khomeini, in Mecca back in 1963, and I believe that Maududi had a great influence on Khomeini's Islamist thinking. In 1979, Maududi and the Muslim Brotherhood endorsed the Islamic revolution in Iran whole-heartedly.

In the 1980s, some Sunni jihadis saw Shiite jihadis as their geopolitical rival. The Iranian recruiting of fighters in countries like Afghanistan and Pakistan will certainly exacerbate the situation.

Read: Pakistan must not allow extremists to act as a 'Sunni Wall' against Iran

What will be the impact of the tug-of-war between Riyadh and Tehran on countries like Pakistan and Afghanistan that have a mixed Sunni-Shiite population?

Afghanistan is a very interesting case in this regard, as the Sunni jihadi group, the Taliban, is increasingly relying on Iranian support and has built alliances with local Shiite militias. Gulbuddin Hekmatyar, a Sunni warlord, was closer to Pakistan in the past but has been aligned with Tehran for the past 25 years.

Paulo Casaca is founder and executive director of the Brussels-based South Asia Democratic Forum (SADF). He was a Portuguese member of the European Parliament from 1999 to 2009. Casaca is the author of several books and reports on economics and international politics.

The interview was conducted by Shamil Shams.