International election monitors on Monday said a weekend parliamentary poll in Kazakhstan lacked any real competition, raising concerns over freedom of assembly after riot police detained opposition protesters.

Sunday's vote in the authoritarian Central Asian country went ahead without any genuine opposition parties, even after leader Kassym-Jomart Tokayev promised gradual reforms after he came to power in 2019.

"As all political parties contesting the elections supported the policies of the ruling party, the campaign was not competitive, and voters had no genuine political alternatives to choose from," the Organization for Security and Cooperation in Europe (OSCE) said in a statement.

Election officials in the ex-Soviet country confirmed Monday that the ruling Nur Otan party had won with 71 percent of the ballot, while the only true opposition group boycotted the vote in protest.

An EU spokesman said the European Union appreciated "the efficient organisation" of the elections but noted a "missed opportunity" to demonstrate the strength of some political reforms and modernisation processes made since the last parliamentary vote.

No previous vote in Kazakhstan has been described as free or fair by the OSCE, which said Monday that previous recommendations to improve fundamental freedoms had not been addressed.

"Curbs on the freedom of association, of assembly and of expression had a negative impact on campaign activities, which remained low key in the run-up to election day," it added.

Dozens of anti-government activists were detained after polls opened despite a pledge by Tokayev that police would treat protesters "within the framework of the law".

Riot police surrounded two groups of several dozen protesters for several hours in frosty conditions in the largest city Almaty.

Representatives of international rights groups including Human Rights Watch and the Norwegian Helsinki Committee were quick to condemn the tactic, known as "kettling".

Law enforcement officers detained opposition supporters during a rally as Kazakhstan held a parliamentary election
Law enforcement officers detained opposition supporters during a rally as Kazakhstan held a parliamentary election AFP / Ruslan PRYANIKOV

One prominent activist, Zhanbolat Mamay, who said he was trapped inside the police cordon for most of the day, told AFP that "dozens" of his unregistered group's supporters had been arrested and taken to police stations.

Police later said they had released everyone and had not brought any charges against the demonstrators.

The activists were detained "for attempts to organise illegal rallies and marches", deputy interior minister Arystangany Zapparov said, without giving figures.

Tokayev, 67, has pledged greater transparency after he was ushered into the presidency by former leader Nursultan Nazarbayev, who called time on nearly three decades in the role in early 2019.

Nazarbayev, who is chairman of Nur Otan, said on Sunday that exit polls showed how citizens "associate the further development of our country and the improvement of (their) welfare with our party".

The two parties that joined Nur Otan in parliament -- Ak Zhol and the People's Party of Kazakhstan (PPK) -- were already in the legislature and widely viewed a loyal to the government.

"There are three Nur Otans in parliament," joked Darkhan, a taxi driver in Almaty on Monday. "They don't differ from each other. Even some of our government opponents are Nur Otan. Nur Otan is everywhere."

The PPK had styled itself as a communist party until late last year when it underwent a rebranding.

Self-styled opposition group, the National Social Democratic Party, boycotted Sunday's vote, having missed out on the legislature every time after competing in the last three parliamentary elections.