Eighteen opposition lawmakers were detained in Montenegro's parliament on Friday for their involvement in violent protests against a controversial religious law.

The law, which was passed shortly after the MPs were detained, includes a clause requiring religious groups to prove ownership of properties from before 1918, when Montenegro joined a Serb-led Balkan kingdom and lost its independence. It was passed in the early hours on Friday with 45 of 81 total members voting in favor of the bill.

Six other people, who were not opposition MPs, were also detained, bringing the total to 24. All but three of the lawmakers were later released. The three are suspected of attacking the parliament speaker and preventing him from performing his job, according to state television station RTCG.

Read more: Montenegro's fractious opposition takes to the streets

In a remarkably tense string of protests and debates, MPs from the opposition party Democratic Front, threatened armed violence if the law was passed.

"We are ready to die for our church and that's what we are demonstrating tonight," said opposition leader Andrija Mandic.

After their party's proposed amendments to the law were rejected, the MPs vandalized the parliament building, hurled a tear gas canister and plastic bottles, and attempted to attack other politicians.

Read more: Montenegro opposition leaders jailed for pro-Russian coup plot

Prime Minister Dusko Markovic decried what he called "irresponsible" chaos in the assembly, adding that he believes "this kind of incident will not be repeated."

The law has inflamed tensions in recent weeks between the government and pro-Serb opposition, which has strong ties with the Serbian Orthodox Church (SPC), Montenegro's primary religious branch.

In a statement, the SPC called the law "discriminatory and unconstitutional," and accused the Montenegran government of "inciting divisions and hatred."

They added that the Serbian Orthodox Christian community would face "one of the saddest Christmases in recent history."

The SPC, which controls hundreds of monasteries throughout the country, says it will strip the church of its rights to its property, including churches and medieval monasteries — a claim the ruling party denies.

Nearly 72% of Montenegro's population of around 620,000 identifies as Serbian Orthodox Christian.

Montenegro was part of the same country as Serbia until it became independent in 2006. About a third of Montenegrins still identify as Serbs, according to the 2011 census, and the population remains divided over whether the country should carry on its ties with Serbia.

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lc/sms (AP, AFP)