KABUL - Afghanistan's school year started on Tuesday, the education ministry said, as the U.N. children's agency renewed calls for teenage girls to be able to rejoin the classroom.

A year ago, after signalling that they would open schools for all students, Taliban authorities made a U-Turn, leaving many girls who had turned up to their high school classes in tears and sparking global condemnation that has hampered the Taliban's efforts to gain formal international recognition.

Since then primary schools for girls have stayed open but most high schools have been closed and the Taliban barred female students from university in December, provoking international outcry and protests In some Afghan cities.

A letter from the education ministry confirming the official start of the school year after the winter break this week made no mention of any change in access for girls. The head of the U.N. children's agency in Afghanistan said authorities needed to open schools to all students so they could resume socialisation and building skills as well as academic learning.

"As the new school year in Afghanistan begins, we rejoice in the millions of boys and girls returning to primary school classrooms. Yet, we are deeply disappointed not to see adolescent girls going back to their classrooms as well," said Fran Equiza, UNICEF's Afghanistan representative, in a tweet.

As many Afghan women have continued calling for schools to re-open, enrolment at female religious schools - the only remaining option - has gone up over the past year.

In Kunduz province, one of a handful of northern provinces where some girls' high schools had quietly remained open last year, authorities said they were closed for now.

"This year the schools are open up to class six for girls, we are waiting for further notice about secondary classes," Mohammed Ismail Abu Ahmad, the head of Kunduz's education department told Reuters.

In the capital Kabul, school openings appeared limited on Tuesday which fell on Nowruz, the Persian New Year that is widely celebrated in Afghanistan and which had previously been a public holiday.

Taliban authorities said last year that they would not recognise Nowruz as a public holiday, though they had not barred people from celebrating privately.

(Reporting by Mohammad Yunus Yawar; Writing by Charlotte Greenfield Editing by Tomasz Janowski)