Ban Ki-moon is on a six-day tour of Central Asian nations
UN Secretary General Ban Ki-moon has called on Uzbekistan to improve its human rights record.
Speaking in Tashkent, Mr Ban said Uzbekistan had to put the international agreements it had signed on torture and civil rights fully into practice.
Rights groups and western countries have accused Uzbek authorities of abuses, including torture, and repressing political dissent.
President Islam Karimov, who later met Mr Ban, denies there are such abuses.
Mr Ban is on a six-day tour of Central Asian nations.
On Sunday he visited the Aral Sea - the once-vast lake that has shrunk to about 10% of its original size as a result of Soviet-era irrigation projects.
Calling it one of the world's worst environmental disasters, Mr Ban promised UN assistance in dealing with the catastrophe.
'Time to deliver'
Mr Ban's visit to Uzbekistan came less than two weeks after the country was criticised in a report by the UN Human Rights Committee.
Mr Ban visited the Aral Sea, calling it an environmental disaster
The committee said Uzbekistan had failed properly to investigate a bloody government crackdown on protesters in Andijan in 2005.
It also expressed concern over reports of torture by security personnel, the harassment of journalists and activists, and queried the independence of the judiciary.
Mr Ban did not give specific examples, but he told students at a university in Tashkent that it was time for the country to make progress.
"You have an important place in the universal agreements that bind us as a community of nations," he said. "It is time to deliver. To put them fully into practice."
He later met Mr Karimov, who has ruled Uzbekistan for two decades, telling him he expected the government to "lead by example".
Mr Ban is now travelling to Tajikistan.