Iranian chess officials have barred two teen siblings from domestic chess tournaments and the national team for crossing some of the religious establishment's so-called red lines at an international chess event.

The Iranian National Chess Team dismissed 18-year-old Dorsa Derakhshani for appearing at the Tradewise Gibraltar Chess Festival 2017, which ran from January 23 to February 2, without the Islamic head scarf that became compulsory in Iran after the 1979 Islamic Revolution.

Her 15-year-old brother, Borna Derakhshani, was banned for playing against an Israeli opponent at the same event.

Iran does not recognize the state of Israel and forbids Iranian athletes from competing against Israeli athletes at international sports events. Iranians in the past have cited injury or illness to avoid facing Israeli rivals.

Last year an Iranian refused to compete against an Israeli at a chess tournament in Switzerland in order to reject the existence of "the Zionist state" and to express support for the "oppressed people of Palestine," the semiofficial Mehr news agency reported.

The measures against the Derakhshanis were announced by the head of the Iranian Chess Federation, Mehrdad Pahlevanzadeh, on February 19.

"As a first step, these two will be denied entry to all tournaments taking place in Iran, and, in the name of Iran, they will no longer be allowed the opportunity to be present on the national team," Pahlevanzadeh told the semiofficial Fars news agency.

Pahlevanzadeh said the pair had attended the Gibraltar event independently rather than representing Iran. "Anyone can participate in it," he said.

He suggested that the teens had hurt Iranian national interests.

"Unfortunately, what shouldn't have happened has happened. Our national interests have priority over everything," Pahlevanzadeh said. He added that there would be no "leniency" for those who trample on Iran's "ideals and principles."

"We're considering measures that will prevent similar incidents from taking place in future tournaments," he told Fars.

Borna Derakhshani reportedly lives in Iran. His sister studies in Spain.

The two have not reacted publicly to the ban.

Iran enforces a dress code that requires women to cover their hair with the Islamic head scarf, or hijab, through regular crackdowns. Female officials, athletes, and other national representatives are required to respect the hijab guideline while traveling abroad, too.

Last year Minoo Khaleghi, who was elected to the Iranian parliament, was barred from taking her legislative seat after reports that photos emerged on social media showing her without a head scarf during a trip to Europe and China.