Pakistani Prime Minister Imran Khan arrived in Iran on Sunday on a two-day official visit to the neighboring country.

He was scheduled to meet with Iranian President Hassan Rouhani on Monday. Pakistani officials say the two leaders will discuss a range of topics, including an expansion of bilateral trade and the issue of militancy along the two countries' shared border.

The state-run IRNA news agency said Khan's trip was expected to help "develop ties between the two countries, especially those related to regional cooperation in fighting terrorism and safeguarding borders."

But ties between Iran and Pakistan have remained tense due to a deep mistrust of each other. Pakistan has generally tried to maintain close ties with both Saudi Arabia and Iran — bitter regional foes — but has drifted away from Tehran in the past few years.

Both countries accuse each other of backing separatist groups, which are active in Pakistan's and Iran's Baluchistan provinces and seek independence from both countries.

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Accusations and counter-accusations

In March, President Rouhani demanded Pakistan act decisively against anti-Iranian terrorists, following a February attack that killed 27 members of the elite Revolutionary Guards in Sistan-Baluchistan. Iran claimed that a Pakistani suicide bomber was behind the attack, which was claimed by the Sunni jihadist group Jaish al-Adl (Army of Justice), which Tehran says operates mostly out of Pakistan.

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On Saturday, Pakistan's Foreign Minister Shah Mahmood Qureshi said that "terrorist outfits" that carried out a deadly attack against armed forces on Thursday had crossed the border from neighboring Iran.

The killings took place when they were traveling in buses on the Makran coastal highway between the southern city of Karachi and Gwadar in the southwest, a key port in China's multi-billion dollar China-Pakistan Economic Corridor (CPEC) project. The gunmen reportedly entered the bus, demanded to see everyone's IDs, and then commenced their attack on specific passengers. Those killed included 10 serving in the navy, three working with the air force and one with the coastguard.

Ties between the two neighboring countries have been tense for many years. Shiite-majority Iran is wary of Islamabad's alleged support to various Sunni militant groups, which have been involved in launching attacks in Iran's eastern areas, and massacring Shiite citizens inside Pakistan.

The sectarian strife in Pakistan has been ongoing for some time now, with militant Islamist groups unleashing terror on the minority Shiite groups in many parts of the country. Most of these outfits, including the Taliban, take inspiration from the hardline Saudi-Wahabi Islamic ideology.

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On April 12, militants killed at least 16 people in a powerful blast targeting the Shiite Hazara ethnic minority Baluchistan's capital city Quetta.

'Solidly allied with Riyadh'

Iran is also angered by Pakistan's role in the Saudi-led military alliance that is operating against Shiite Houthi rebels in Yemen.

"It is obvious that the Pakistani-Iranian ties have not been cordial for quite some time. However, if the Pakistani government gives more importance to Saudi Arabia in the Yemen conflict, the relations will likely get acrimonious," Tariq Peerzada, a foreign affairs expert in Islamabad, told DW.

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Earlier this year, Saudi Crown Prince Mohammed bin Salman visited Islamabad and was received enthusiastically by PM Khan and other Pakistani officials. Khan reiterated his country's pledge to stand behind Riyadh in regional conflicts.

Islamabad's over-enthusiasm to please Riyadh could further exacerbate its relations with Tehran. Security analysts say that Pakistan's support to Saudi Arabia has increased the Sunni-Shiite rift in the South Asian country. They also say that Sunni militant groups feel further emboldened by the fact that Raheel Sharif, Pakistan's ex-army chief, now heads the Saudi-led military alliance.

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Tehran is aware of Islamabad's cooperation with Riyadh. At the same time, it is aware of the concerns and limitations of its ties with Pakistan and wants to maintain "normal" relations with the neighboring country.

"Pakistan remains solidly allied with Saudi Arabia, regardless of how intense the outreach may be from Tehran. There are decades of close military cooperation that are not about to undone," Michael Kugelman, a South Asia expert at the Washington-based Woodrow Wilson Center for Scholars, told DW.

It remains to be seen whether Pakistani leader Khan could convince Iranian authorities that his country would not undermine Tehran's interests in the region. But since Pakistan is already part of the Saudi security alliance and has not done enough to allay Iran's concerns about its alleged role in backing anti-Iran militants on its soil, experts say that Khan's diplomatic efforts in Tehran are unlikely to yield results.

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