Azerbaijan's strained relations with Iran aren't getting any better. Baku has sent two protest notes to Tehran in recent days.  

On March 11, Azerbaijan's foreign and defense ministries said in a joint statement that a military aircraft belonging to Iran flew non-stop along much of the length of the Azerbaijan-Iran state border from the direction of Zangilan district to Bilasuvar district and back. The route included several districts that Azerbaijan retook from Armenian forces in the 2020 Second Karabakh War. 

"Contrary to the internationally accepted practice of warning the neighboring country in advance about approaching military aircraft to the state border, such a close proximity of a military aircraft of the Islamic Republic of Iran to the state border between the two countries and flying over the border line threatens the safety of civil aviation, and further deteriorates bilateral relations," the English statement read. 

"The flight of a military aircraft for more than half an hour near the liberated territories of Azerbaijan is a provocation and unfriendly behavior towards Azerbaijan." 

It added that the Iranian ambassador to Azerbaijan, Seyyed Abbas Mousavi, had been summoned to the Foreign Ministry and was handed a note of protest.

Iran responded publicly two days later when Foreign Ministry spokesman Nasser Kanaani said the flight was routine and took place well inside Iranian territory. By publicly protesting the flight and summoning the ambassador, Baku was "acting not in good faith" and "outside the bounds of normal relations between countries, especially neighboring countries," he said.

Earlier, on March 9, the spokesperson of Azerbaijan's Foreign Ministry, Aykhan Hajizade, told local media that Azerbaijan sent a note to Iran and was awaiting answers regarding the whereabouts of an Azerbaijani citizen who was lost in Iran. Farid Safarli, 26, had been in Iran since February 20 and was supposed to fly to Germany on March 4, but since then there has been no news of him, Hajizade said. 

Azerbaijan's Foreign Ministry advised citizens "not to travel to Iran unless necessary, and those who do travel to show high caution" on January 27, after a deadly attack by a gunman on its embassy in Tehran. 

Following the embassy attack, where the security chief was killed and two officers were wounded, Azerbaijan evacuated its embassy staff, effectively scaling back diplomatic relations. 

On February 17, Azerbaijan President Ilham Aliyev directly blamed "some branches of the Iranian establishment" for the attack and told journalists that the relations between the two countries could be normalized only after those responsible are brought to justice. 

The embassy attack was the most dramatic single incident in a deterioration of Baku-Tehran ties that has been going on for years. Azerbaijan has long accused Iran of favoring Armenia in the decades-long conflict over Karabakh – especially after the 2020 war, when Azerbaijan established control over its entire frontier with Iran.

Since then, Azerbaijan has regularly accused Iran of sending weapons to Armenians in Karabakh, and the two countries have repeatedly held military training along their shared border.

Another, related, factor in the tensions is Azerbaijan's warm ties with Iran's archrival Israel. 

Azerbaijan's active military cooperation with Israel -- whose extent was outlined in a recent article in Haaretz -- was instrumental in Baku's victory in the 2020 war. Tehran worries that Israel uses Azerbaijan as a base for gathering intelligence on Iran and views it as a staging ground for possible future attacks. 

A day before the controversial border flight, on March 10, Azerbaijani President Aliyev had a meeting with Israeli Intelligence Minister Gila Gamliel in Baku. 

Meanwhile, Azerbaijan continues to detain alleged Iran-backed agents of destabilization. On March 13, the pro-government news agency APA reported that 32 people "who carried out acts of sabotage and disruption under the guise of religion were identified and detained," though the news has yet to be confirmed by law enforcement. 

"Investigators established that they organized the sale of narcotics sent purposefully from the Islamic Republic of Iran and used the huge amount of money they got to promote religious radicalism in Azerbaijan and finance other disruptive activities," the report read.