Authorities in Uzbekistan said Saturday that they had arrested "organisers of mass riots" who wanted to seize administrative buildings in an autonomous republic that witnessed rare protests over constitutional reform proposals.  

The Friday demonstration in the Republic of Karakalpakstan brought thousands onto the streets of the regional capital and followed the publication of draft amendments to the Uzbek constitution that weaken the republic's status and should go to referendum in the coming months.

Spontaneous demonstrations are illegal in the authoritarian ex-Soviet republic and police said Friday that "order had been restored" in the area taken over by the demonstration.

The tightly controlled government has made no mention of casualties.

The proposed constitutional changes will strip the Republic of Karakalpakstan of its nominal "sovereign" status and remove its constitutional right to secede from Uzbekistan via referendum.

Constitutional commission member and lawmaker Odiljon Tozhiyev said Saturday that the commission was observing the situation in the republic and would take opinions expressed online in the republic into account.

Nevertheless, "provocateurs who tried to cause riots do not represent the general opinion of the Karakalpak people", Tozhiyev said.

Authorities in Karakalpakstan, who are beholden to central government despite legal autonomy, have taken a harder line.

A joint statement by the republic's police, parliament and cabinet said that "provocateurs" had attempted "to seize state institutions... split the society and destabilise the socio-political situation in Uzbekistan".

"A group of organizers of mass riots and people who actively resisted law enforcement agencies have been detained. Investigative actions are underway against them," the Saturday statement said, blaming unrest on a "criminal group".

Internet has been patchy in the Republic of Karakalpakstan, a western region of two million people that has been devastated by the drying of the Aral Sea. Once the world's fourth largest lake, it shrank massively due to Soviet agricultural policies.

With a total population of 35 million people, Uzbekistan is Muslim-majority Central Asia's most populous country.

Beyond changes to the region's status, Uzbekistan's new constitution is also expected to re-introduce seven-year terms for the presidency, benefitting strongman Shavkat Mirziyoyev and harking back to the era of his despot predecessor and mentor Islam Karimov.

Mirziyoyev campaigned for and won re-election last year under a "New Uzbekistan" campaign slogan, but critics accuse Tashkent of backsliding on rights after introducing economic and social reforms.