Anglo-Russian Rivalry was a factor in the slow development of Iranian railways.
An online source drawing from an article in Railway Magazine (Jan 1963), by M.A. Baker, provides the following background information which indicates that the Persian government was itself, in part responsible for the slow development of rail in their country:
Until the 1930s, Iran was relatively isolated, but from around 1865
various European Countries had sought concessions to construct
railways but the Imperial government continued to value isolation
above integration.
Baker says that, “Shah Naser-ed-Din … was so delighted with railways
that he determined to have one built in Iran.” [1: p21] Shah
Naser-ed-Din reigned from 1831 to 1896. He was the first modern
Iranian monarch to formally visit Europe. He wrote travelogues about
his trips, that also were translated in foreign languages. 2
Shah Naser-ed-Din called on a French engineer and concession hunter,
Fabius Boital, to build a line from Tehran to the shrine of Abdul Aziz
at Rey, 6 miles south of the city. He also received a concession to
build tramways in Tehran.
It would appear, in addition however, that the Russians and British did also hinder the development of railways in Persia due to their shared concerns about the introduction of a "speedy means of communications connecting the north and south of Persia". It also appears from the following source that the difficulty in actually building a railway in such a remote location, and the likely need to use ports and infrastructure controlled by Russia or Britain to enable construction to proceed was a limiting factor, which enabled those two countries to restrict development.
One of the locomotives built in Belgium in 1887 (Railways in Iran)
During the three decades between the 1850s and the 1880s various
French, Belgian, British, Russian and American concerns attempted to
introduce railways to Persia, but these did not materialize, either
due to lack of adequate capital or because of the Anglo-Russian
rivalry (Jamālzāda, pp. 87-88; Lorini, pp. 158-59; Maḥbubi Ardakāni,
II, pp. 321-24). In December 1886, a French engineer and
concession-hunter by the name of Fabius Boital received a concession
from Naṣer-al-Din Shah to build a small Decauville railway from the
capital Tehran southwards to the Shrine of Šāh ʿAbd-al-ʿAẓim, a
popular site of pilgrimage in Ray, a distance of about 6 miles. In
addition, Boital received a concession for the construction of
tramways in Tehran (Churchill, 27 Aug. 1888 p. 16; “Memorandum on
Persian Railways”). Probably due to a shortage of money, Boital sold
both concessions to a Belgian company named “La Société Anonyme des
Chemins de Fer et Tramways en Perse,” founded in Brussels on 17 May
1887. The company had a capital of 2 million francs (“Acte,” p. 865).
The rail concession provided the Belgian company with the exclusive
rights to construct and operate a railway line from Qazvin to Qom
through Tehran and Šāh ʿAbd-al-ʿAẓim for 99 years (“Concession,” p.
45). The president of its executive board was Edouard Otlet
(1842-1907), a Belgian international businessman with a great deal of
experience in railroad construction in both Europe and the United
States.
Although the large number of pilgrims (over 300,000 per annum) who
visited the shrine (Curzon, I, 617) promised handsome returns for the
company, its executives wanted much more: a railway line connecting
the Caspian Sea and the south, and passing through Tehran (Otlet à
Barbanson). This did not materialize because speedy means of
communications connecting the north and south of Persia ran contrary
to both British and Russian interests (d’Erp à Caraman Chimay; Wolff
to Salisbury, 25 April 1890).
The task of constructing the line was very difficult since the Belgian
company needed to transfer all the necessary equipment - rails, 21
wagons, 4 steam locomotives, etc. - all by sea from Antwerp to Batum
on the Black Sea, then by land through the Transcaucasian Railway to
Baku, then by sea again to Anzali on the Caspian Sea, and from there
once more by land and on the back of animals, through difficult
terrain, to Tehran through Qazvin. The weather, customs clearance,
shipments and re-shipments, were part of the other difficulties, which
the Belgian team, headed by the engineers Guillon, Denis, and Julien,
had to face (“Le premier chemin de fer en Perse,” p. 1; “Rapport,” pp.
3-5; Beyens, p. 14; Curzon, I, p. 617). In order to minimize the
difficulties involved in the cumbersome process of shipping from
Belgium to Persia, Denis established a workshop in Baku for packing
the material from Belgium, bought animals from Tbilisi for
transportation, purchased part of the rails from Russia, built boats
for river transport, and employed local workers for maintaining the
roads. By these steps he was able to transfer more than 1,000 tons of
equipment from Raštto Tehran, but these measures proved very costly.
(“Rapport,” pp. 5-6; Curzon, I, p. 617).
Sources:
Railways in Iran – Part 1 – Tehran to Rey 1888 (Roger Farnworth)
Drawing upon information from Railway Magazine (Jan 1963).
Railroads i. The First Railroad Built and Operated in Persia (Encyclopedia Iranica)
Details of the various references cited above can be found in the link.