Tensions are rising between Tehran and Baku amid mutual accusations that each has sponsored terrorist activities on the other's soil.
Iran and Azerbaijan in spy feud
Azerbaijan, a small oil-rich country tucked between Iran and Russia, has emerged as a key hub for cloak-and-dagger spy wars being waged between Iran and the West over Tehran's nuclear programme.
Iran's foreign ministry summoned the Azerbaijani ambassador on Sunday, accusing his country of assisting Mossad, Israel's intelligence agency, in the assassination of an Iranian nuclear scientist last month. Mostafa Ahmadi-Roshan, who worked at Iran's Natanz uranium enrichment facility, was killed when two men on a motorcycle attached a magnetic bomb to his car.
At least four scientists associated with Iran's nuclear activities have been murdered in similar, highly professional hits since 2010.
Iran's supreme leader, Ayatollah Ali Khamenei, accused the United States and Israel of Mr Ahmadi-Roshan's "cowardly" killing. Washington vehemently denied responsibility and condemned the assassination. Israeli officials do not comment on whether they are behind the killings of Iranian scientists but have made clear their satisfaction.
Azerbaijan yesterday rejected Iranian allegations that Baku helped in any of the assassinations as "slander". The Iranian complaint, it said, was retaliation for a formal protest by Azerbaijan to Tehran last month that Iranian agents had plotted to kill Israel's ambassador in Baku along with a rabbi.
Azerbaijani authorities have also said they thwarted a plan by agents of Iran and Lebanon's Hizbollah militia to set off a car bomb near the Israeli embassy four years ago, and a plot targeting the US and British embassies in 2007.
A Mossad operative in the Azeri capital, Baku, told The Times at the weekend: "This is the ground zero for intelligence work". The London daily described him as one of dozens of Mossad agents who work in Azerbaijan at any given time. Numerous members of Iran's Revolutionary Guard are also said to operate in Baku.
Azerbaijan, a secular Muslim former Soviet republic, has friendly ties with the US and Israel and is home to more than 9,000 Jews. Israel imports 30 per cent of its oil from Azerbaijan which in turn imports weapons and military hardware from the Jewish state.
The US has built a large installation in southern Azerbaijan to monitor Iran, and has another one in the north to monitor Russia, Azeri officials told The Times.
Diplomatic relations between Iran and Azerbaijan have long been cool. Baku is aggrieved by Iran's support of Christian Armenia, with which Azerbaijan has had a long territorial dispute. It also accuses Tehran of sponsoring Islamic radicals in Azerbaijan.
Iran, in turn, accuses Baku of stoking unrest among its large ethnic Azeri minority, which far outnumbers Azerbaijan's own population of 9.2 million.
Another intriguing and controversial slant on the killing of Iranian nuclear scientists came from a major US news network in a detailed report last Thursday. NBC was told by US officials that the deadly attacks were being carried out by an exiled Iranian dissident group that it said is financed, trained and armed by Mossad.
The People's Mujahideen of Iran, or MEK, is classified by the US as a terrorist organisation. The group is linked to the deaths of at least six Americans in Iran during the 1970s and supported the takeover of the US embassy in 1979 before it fell out with the revolutionary new regime in Tehran.
The MEK was long allied with Saddam Hussein's Iraq, which provided it with shelter and arms, making it deeply unpopular with most ordinary Iranians.
The organisation has denied the NBC allegations of collaboration with Israel as "absolutely false".
Israel declined to comment on the NBC report.