The presidents of Russia, Iran and Azerbaijan signed a declaration on Monday to boost ties in defence and commerce in the Caspian Sea region.
The declaration foresees strengthened ties in anti-terrorism efforts and work towards resolving regional conflicts, as well as other spheres such as energy and transportation, Russian state news agency TASS reported.
Earlier in the day, Russian President Vladimir Putin praised bilateral ties with Iran. He had announced last week that Russia would build eight more nuclear reactors in that country.
Since Putin visited Tehran last year, "we have made a sizeable path in the development of our bilateral relations," he told Iranian President Hassan Rowhani at a meeting in Azerbaijan's capital, Baku.
"Our friendly relations are strengthening, and it is encouraging to note that they have a diverse character," Putin said, according to a Kremlin transcript.
Putin, Rowhani and Azerbaijan's President Ilham Aliyev participated in a series of meetings on Monday that were set to boost ties across the Caspian Sea region. The event drew to a close with the signing of the trilateral declaration on boosting collaboration.
In an interview published by Azerbaijani state news agency AZERTAC ahead of the meetings, Putin said Russia plans to build eight more nuclear reactor units in Iran and also intends to lend Iran 2.2 billion euros (2.5 billion dollars) for financing energy projects.
Russia previously helped Tehran construct its major power plant near the city of Bushehr. In 2014, Russia signed a deal to build two more reactors at the facility.
Rowhani told Putin on Monday that Iran "will never forget the positive role that Russia played in reaching the nuclear agreement," referring to an international deal on regulating the Islamic republic's nuclear programme that allowed sanctions to be lifted.
Rowhani said he was pleased that commerce with Russia has been growing and lauded Monday's meetings as a way to improve relations and strengthen regional stability.
Aliyev also commended Russia's role in seeking peace for the disputed Nagorno-Karabakh region, over which Azerbaijan and neighbouring Armenia have clashed for decades, with a deadly surge in violence earlier this year.
"I would like to especially underline Russia's role in resolving the Armenian-Azerbaijani conflict over Nagorna-Karabakh," Aliyev told Putin, according to a Kremlin transcript. "We value this role, and your personal participation plays a very important role in the peace process."