The Iranian capital is one of three co-host cities for the second stage of the flagship event, with teams from Serbia, Argentina and Italy, as well as the host nation, all competing there.

But the build-up was dominated once again by criticism over the ban surrounding female spectators, first introduced at volleyball matches in the Islamic country in 2012 as an extension of a similar ban in football.

Women attempting to buy online tickets have repeatedly received messages saying they were unable to purchase, with human rights groups claiming only specially selected groups would be permitted.

Female-only areas were full today as action began, with this hailed as a key "first step" by the FIVB.

"The attendance of women at the opening matches of the World League in Tehran on Friday is a first step of a long-term campaign to re-instate female spectators at volleyball events in Iran and one which the FIVB is 100 per cent committed to," a spokesperson told insidethegames today.

"Our policy is one of engagement and diplomacy to secure inclusion through sport not through the threat of isolation."

The law generated worldwide condemnation in 2014 following the arrest of British-Iranian woman Ghoncheh Ghavami during a World League match.

Ghavami, arrested for "propaganda against the regime", spent 151 days in Evin prison before she was released and charges eventually dropped. 

The FIVB has repeatedly pledged to have the ban lifted before this year's Olympic Games in Rio de Janeiro, but have proved unable to do so in the face of religious and political opposition.

They told insidethegames in April that they were switching to an "event by event" approach rather than a blanket lifting of the ban.

The world governing body provoked more criticism, however, by continuing to award events to Iran despite initially claiming they would not, insisting that the incentive of hosting competitions will be the best way to encourage progress.

Some women were turned away during a beach volleyball World Tour event in Kish Island in February, although others attended and the FIVB claimed the problems were only due to a "misunderstanding".

“'No discrimination'” is one of FIVB’s 'fundamental principles' in its constitution (Section 1.5.4)," said an open letter from Human Rights Watch to FIVB President Ary S. Graça, dated May 31.

"In view of the blatant gender discrimination and exclusion of female spectators at the FIVB’s last three tournaments in Iran, we strongly urge the FIVB to: Investigate the exclusion of female spectators during the volleyball games on Kish Island in February.

"Urge Iranian authorities to repeal the ban, prior to the FIVB World League matches in July 2016.

"Ask Iranian volleyball officials to announce publicly how women can buy tickets online and attend these matches.

"Request that Iranian authorities issue instructions to security officials at the games, and to all other law enforcement bodies, to ensure that women and girls can safely attend volleyball matches.

"Declare that Iran will not be allowed to host future FIVB tournaments unless women can safely attend men’s volleyball matches."

Italy opened proceedings at the Azadi Indoor Stadium today with a 25-18, 25-20, 22-25, 25-22 victory over Argentina.

Iran then superbly recovered from 2-0 down to beat Serbia 18-25, 22-25, 25-22, 25-23, 16-14.

Matches have also taken place today at the Palais des Sports Jean Weille in Nancy, where Brazil showed ominous pre-Olympic form in a 30-28, 25-21, 25-16 victory over Poland.

France were similarly comfortable in dispatching Belgium 25-19, 28-26, 25-20.