Azerbaijani President Ilham Aliyev's absence from a regional summit hosted by Turkey on Friday has fuelled speculation about growing tensions between the two traditionally close allies.
Turkey and Azerbaijan share strong ethnic and cultural ties and frequently describe their relationship as "one nation, two states." However, recent disagreements over Azerbaijan's decision to prohibit Islamic headscarves in schools and its close relationship with Israel have strained ties.
Aliyev's participation in the Organization of Turkic States summit in Ankara was closely watched for signs of the relationship's condition. Azerbaijan was represented by Foreign Minister Jeyhun Bayramov, while Azerbaijani media reported that Aliyev had prior commitments.
The organisation comprises Turkey, Azerbaijan, Kazakhstan, Kyrgyzstan and Uzbekistan.
Farman Aydin, an analyst writing for the pro-government Azerbaijani outlet Azernews, pointed to what he described as an increasingly hostile campaign against Azerbaijan in Turkey. He said Aliyev's absence could signal that even close partnerships require mutual respect.
Tensions intensified in September after Turkish social media users and members of President Recep Tayyip Erdogan's ruling party criticised Baku's decision to ban girls and teachers from wearing Islamic headscarves in schools. Small protests also took place outside Azerbaijani diplomatic missions in Turkey, where Erdogan's government lifted similar restrictions after coming to power in 2003.
Turkey's criticism of Azerbaijan's close ties with Israel has further complicated relations. Ankara has strongly opposed Israel's military actions in the Middle East.
Azerbaijan, an energy-rich country, reacted angrily to what it viewed as interference in its domestic affairs, despite the Turkish government not officially commenting on the headscarf ban. Baku subsequently barred more than 30 Turkish nationals, including the leader of a small Islamist-oriented opposition party, from entering the country over their criticism.
Seeking to ease tensions, Erdogan personally called Aliyev earlier this week to invite him to the summit. Turkish media also reported that Erdogan dismissed an aide, Oktay Saral, following an apparent demand from the Azerbaijani president.
Opening the summit, Erdogan stressed unity among Turkic-speaking nations, saying there was no place for division or disputes within the Turkic world.
The strained relationship could also affect Turkey's efforts to normalise ties with neighbouring Armenia. Ankara closed its border with Armenia in the 1990s in support of Azerbaijan during its conflict with Armenia and has linked normalisation to progress in Armenian-Azerbaijani reconciliation.