President Ilham Aliyev skipped a summit of Turkic states on Friday despite a personal invitation from his Turkish counterpart, highlighting growing tensions between the historic allies over domestic and regional policies.

Ties between Turkey and Azerbaijan have become strained in recent weeks over some Turkish officials' criticism of Baku's decision to impose restrictions on the use of headscarves under new secular school uniform regulations.

Aliyev and other Azeri officials warned against interference in Baku's affairs, without mentioning Turkey — a rare crack in an alliance of nations at the heart of a fractured region. Any worse break could hurt Turkey's ambitions of increasing its influence in an area where Russia traditionally holds sway.

The two countries are also at odds over Israel. Ankara is a fierce critic of Israel over the war in Gaza, while Azerbaijan has strong ties with it.

Turkish officials have sought to downplay tensions and Erdogan delivered a message of unity at the opening of Friday's summit of countries united by language, culture and roots.

"There is no place for separation, division, or conflict in our family picture. We are all one, together and, God willing, we are brothers forever," he said at the meeting in Ankara, without naming Azerbaijan.

Foreign Minister Jeyhun Bayramov represented Azerbaijan at the summit. Speaking after Erdogan, he did not mention the tensions, thanking Turkey for its hospitality.

The tensions are unusual. The two countries describe their relationship as "two states, one nation". Ties deepened after Turkey backed Azerbaijan during the 2023 Nagorno-Karabakh war and they have built strong ties in defence and energy. Ankara is a major buyer of Azeri natural gas.

Erdogan this week removed one of his advisers, Oktay Saral, after his public criticism of the headscarf decision. He also personally invited Aliyev to the Organisation of Turkic States summit during a phone call last week, according to his office.

The Azeri-Press Agency said, without citing sources, that Aliyev skipped the summit arranged months ago due to "previously planned events and the tightness of his work schedule", including a ceremony and festival at the FIFA U-15 World Cup in Baku.

There has been no official comment from Azerbaijan, while Turkey's presidency and foreign ministry did not respond to requests for comment.

Gonul Tol, director of the Washington-based Middle East Institute's Turkish programme, said that Aliyev skipping the summit was the latest sign of growing tensions between the allies.

"Beneath the 'two states, one nation' rhetoric, tensions have long simmered over a number of issues including Azerbaijan’s sovereignty, Ankara’s influence in Baku, diverging policies toward Israel, and Turkey’s rapprochement with Armenia.

The hijab dispute is a symptom of a deeper rift," she said on Turkey has been working to normalise relations with Armenia but has said that this would depend on peace efforts between Azerbaijan and Armenia. Turkish officials have said Ankara has been looking for progress there so it can take concrete steps like opening borders with Armenia.

Amid the tacit warnings against Turkey, Azerbaijan's foreign ministry this month declared 31 Turkish nationals persona non grata over social media posts criticising Baku.

Turkish Foreign Minister Hakan Fidan said this month after meeting Aliyev at a Baku summit that disinformation was being spread on social media about Turkey-Azerbaijan ties.

He said that while the countries may not agree on everything, they could "sit and discuss our own problems" in a civil way that befits their close ties.

"Can there be different perspectives, different views on certain issues? There can be. Brothers then sit amongst themselves and discuss it in line with their brotherly ties," he said.