Afghanistan's Taliban rulers have banned university education for women nationwide, provoking condemnation from the United States and the United Nations.

Despite promising a softer rule when they seized power last year, the Taliban have ratcheted up restrictions on all aspects of women's lives.

"You all are informed to immediately implement the mentioned order of suspending education of females until further notice," Minister for Higher Education Neda Mohammad Nadeem said in a letter issued to all government and private universities.

The spokesman for the ministry, Ziaullah Hashimi, who tweeted the letter, confirmed the order in a text message to AFP.

Washington condemned the decision "in the strongest terms".

"The Taliban cannot expect to be a legitimate member of the international community until they respect the rights of all in Afghanistan. This decision will come with consequences for the Taliban," Secretary of State Antony Blinken said in a statement.

"No country can thrive when half of its population is held back."

UN Secretary-General Antonio Guterres was "deeply alarmed" by the ban, his spokesman said on Tuesday.

"The secretary-general reiterates that the denial of education not only violates the equal rights of women and girls, but will have a devastating impact on the country's future," Stephane Dujarric said in a statement.

The ban on higher education comes less than three months after thousands of girls and women sat for university entrance exams across the country, with many aspiring to choose teaching and medicine as future careers.

The universities are currently on winter break and due to reopen in March.

After the takeover of the country by the Taliban, universities were forced to implement new rules, including gender-segregated classrooms and entrances, while women were only permitted to be taught by women professors or old men.

Most teenage girls across the country have already been banned from secondary school education, severely limiting university intake. (AFP)