Azerbaijan has gained control of a strategically key and "vast border area" in the Lachin district east of the Zangezur Corridor in the disputed Karabakh region bordering archfoe Armenia, a statement from its Defense Ministry announced Thursday.

"In connection with the commissioning of the new Lachin road, several dominant heights, main and auxiliary roads, as well as a vast border area between the villages of Jagazur and Zabukh, Lachin region, were taken under control," the ministry informed.

The development trails after growing tensions between the neighbors over Armenian military movements in the region, including the transport of personnel and weapons, which Azerbaijan has denounced as a "gross violation" of trilateral agreements Baku and Yerevan inked under the auspices of Russia.

Karabakh was the focal point of two wars that have pitted Armenia against Azerbaijan in the more than 30 years since both ex-Soviet states achieved independence. Russia and Armenia are officially allied through a mutual self-defense pact, but Moscow also seeks to maintain good relations with Azerbaijan.

Karabakh is internationally recognized as part of Azerbaijan but was under Armenian occupation from 1991 to 2020 when a 44-day deadly clash ended with a Russian-brokered cease-fire that saw Armenia cede territory it had illegally occupied for decades and Moscow deploy a peacekeeping contingent.

The agreement is widely regarded as a significant victory for Azerbaijan but it has been broken several times since then, most notably in October when a shootout along their troubled border resulted in the death of over 280 people from both sides.

Since December Baku and Yerevan have been trading accusations over a blockade of the Lachin corridor where Azerbaijani environmental activists have been protesting the illegal mining of Azerbaijani resources in the region. Another flareup in violence in early March saw at least five people killed on both sides on the Khankendi-Khalfali-Turshsu road, which passes north of the Lachin highway.

At the end of the 2020 Karabakh War, the trilateral cease-fire deal included sections on unblocking "all economic and transport routes" in the region, including the connection between Azerbaijan’s western regions and the Nakhchivan Autonomous Republic.

This article encompasses the opening of the Zangezur Corridor, as well.

Today a part of southern Armenia bordering Iran, Zangezur, is the only connection between Azerbaijan and the Nakhchivan Autonomous Republic. The territory was part of Azerbaijan until the Soviets gave it to Armenia in the 1920s and severed Baku’s link with Nakhchivan. During the first Karabakh War in 1992, the railways Azerbaijan built in the region became unusable.

Azerbaijan has been working to restore the railroad and add highways in its Nakhchivan region, including portions crossing Armenian territory. Once those parts are repaired, Azerbaijan could reach Iran, Armenia and Nakhchivan uninterrupted by train.

The corridor would establish a land connection between Azerbaijan and historic ally Türkiye, allowing Ankara to open into Central Asian Turkic states and even Russia.

But Iran, who has strong ties with Armenia, is staunchly opposing the opening of the corridor, according to multiple experts, who argued Tehran is concerned by a possible rapprochement between Armenia, Azerbaijan and Türkiye. Azerbaijani control in Karabakh is already ruffling Tehran’s feathers for what it describes as a "threat" to its access to markets in the Black Sea and Russia.

Armenia and Iran have been discussing plans for an alternative road avoiding Azerbaijan, further stoking tensions between the sides and jeopardizing peace efforts between Baku and Yerevan.

Zangezur, however, is not the only source of conflict between the South Caucasus neighbors.

Relations between Baku and Tehran, which houses a sizable Azerbaijani minority in its northwest, have been strained in recent months after Baku closed its embassy in Tehran due to a terrorist attack that killed the mission’s head of security and wounded two guards in January.

Azerbaijan has also deepened a longstanding relationship with Tehran's rival Israel, which on Wednesday formally opened an embassy in Baku while drawing Iran’s ire.

Furthermore, an Azerbaijani lawmaker with strong anti-Iranian views was wounded in a gun attack at his home on Tuesday this week. Fazil Mustafa, who leads a small opposition party that is seen as ultimately pro-government, has previously called Iran, which shares a Shiite Islamic majority faith with Azerbaijan, a "terrorist state." He has also accused Tehran of trying to turn Azerbaijani religious pilgrims in Iran against the Baku authorities.

Azerbaijan has also accused Iran of providing shelter to and refusing to extradite its citizens that are working to overthrow the government and instigate a regime change in the country, despite requests from President Ilham Aliyev.

At a joint news conference with Iran's foreign minister in Moscow on Wednesday, Russian Foreign Minister Sergei Lavrov too said that he hoped "frictions" between Iran and Azerbaijan would soon be resolved.

"We hope that the current friction in relations between Baku and Tehran is temporary and will be overcome as soon as possible. Russia is ready to provide all necessary assistance for the reconciliation between the two countries," Lavrov said.

Russia maintains friendly relations with both countries.