Pakistan's foreign minister on Tuesday voiced disappointment over the Taliban's ban on university education for women but said the best approach remained engagement with Afghanistan's Islamist rulers.

"I'm disappointed by the decision that was taken today," Foreign Minister Bilawal Bhutto Zardari said on a visit to Washington.

But he said: "I still think the easiest path to our goal -- despite having a lot of setbacks when it comes to women's education and other things -- is through Kabul and through the interim government."

Bhutto Zardari said there were no alternatives to the Taliban, warning of further instability in Afghanistan or the rise of the Islamic State group.

"Is the alternative for us to imagine that we can somehow artificially stitch together an alternate opposition that can command the same sort of legitimacy?"

The Taliban, who had initially promised a softer approach than during their 1996-2001 regime, on Tuesday banned university education for women after already closing down secondary schooling for girls.

The United States, whose troop withdrawal from Afghanistan last year precipitated the collapse of the Western-backed government, warned that the Taliban decision could permanently end any hopes by the militants for a positive relationship.

But Bhutto Zardari said it was even more crucial to ensure economic support "to create the political space necessary for those within the Afghan regime who actually believe that they should deliver" on rights issues.

Pakistan has a complicated relationship with the Taliban, officially backing the two-decade US war in Afghanistan but facing wide accusations in Washington of supporting the militants.