Iranian President Masoud Pezeshkian arrived in Moscow on Friday for high-profile talks with Vladimir V. Putin, his Russian counterpart, cementing the alliance between two countries driven by a shared desire to challenge the West.

Iran and Russia are subject to a series of Western sanctions, and trade and finance are at the forefront of a strategic cooperation agreement that the two leaders are expected to sign.

The accord is expected to cover military issues, but unlike agreements Moscow has signed with other allies, the Iran deal does not include a mutual defense clause, according to Iran’s ambassador to Moscow.

“The independence and security of our country, as well as self-confidence, are very important,” Kazem Jalali told IRNA, Iran’s news agency, TASS reports. “We are not interested in entering any bloc.”

Before Mr. Pezeshkian’s arrival, Dmitri S. Peskov, the Kremlin spokesman, said the signing of the deal would be a “very important event” for Russia, and Iranian leaders portrayed the president’s trip as more than just a state visit, saying it represented a strategic turning point.

“This agreement is not only a key milestone that strengthens our bilateral ties,” Iranian Foreign Minister Abbas Araghchi wrote on the Telegram social network. He added: “This is not just a political agreement, it is a roadmap to the future.”

Mr. Peskov said the timing of the signing was not meant to distract from Monday’s inauguration of Donald J. Trump as president of the United States, and Mr. Araghchi told state television in Iran that the time to sign the contract on Friday was scheduled several months ago.

Since the invasion of Ukraine almost three years ago, Moscow and Tehran have been growing closer. Iran sent short-range ballistic missiles and drones to Russia, according to American and European officials, to help the Kremlin’s war effort. Iran has denied supplying Moscow with weapons.

The Kremlin has provided some diplomatic support to Tehran, but has had to balance that relationship by maintaining ties with Iran’s adversaries, Saudi Arabia and the United Arab Emirates. Both Moscow and Tehran have recently faced major setbacks in the region with the fall of Bashar al-Assad’s regime in Syria.

Since the beginning of the war, Russia has been working to counter what it sees as an aggressive and imperial Western hegemony, led by the United States, by an alliance of countries by creating and formalizing a series of treaties.

In June, Russia signed a partnership agreement with North Korea, and in December, a security agreement with Belarus formalized the deployment of Russian tactical nuclear weapons in that country. Both treaties included a mutual defense clause.

Russia also heads what is known as the Collective Security Treaty Organization, which includes Belarus and several other former Soviet states including Armenia in the Caucasus and Kazakhstan, Kyrgyzstan and Tajikistan in Central Asia. As a counterweight to NATO, the treaty organization is based on the principle that an attack on one member should be understood as an attack on all. The alliance has recently been called into question as Armenia effectively froze its membership.

For its part, Iran faces a series of challenges at home and in the region, with weakened militant allies and a crippled economy due to sanctions. The return of Mr. Trump as US President will bring more pressure and efforts by Washington to isolate Iran.

Beyond defense issues, Russia is working with Iran and other countries to develop an alternative to Swift, the global messaging service that connects more than 11,000 financial institutions and allows them to notify each other of pending transactions.

Moscow is also hoping build a railway through Iran that would connect Russia directly to ports in the Persian Gulf. Mr. Araghchi said the deal would allow Iran to serve as a key gateway for Russian gas exports to the rest of the world through its network of pipelines, bringing gas from the Caspian Sea to the shores of the Persian Gulf. This means, he said, that Iran “is becoming a major hub for gas exports.”

Mr. Jalali, the ambassador to Russia, told Iranian media that the leaders of Russia and Iran realized that the older agreement between the two countries was outdated and did not reflect the reality of the current world and regional order.

The new agreement, he said, “takes into account every aspect of our bilateral relations, including our political posture. How we look at power and how we move forward together.”