Image copyright AFP Image caption MQM lawmakers say their supporters are being victimised

Lawmakers from Pakistan's fourth-largest party, the opposition Muttahida Qaumi Movement (MQM), have resigned from both chambers of parliament.

An MQM leader, Farooq Sattar, said the move was in protest over an army-led crackdown allegedly targeting the party's supporters in Karachi.

The authorities say the action has improved security and is not politically motivated.

The MQM has long denied charges of using violence to control Karachi.

Though currently in opposition, the party has joined governing coalitions at various points in its 30-year history.

The resignation decision applied to the party's 24 MPs in the lower house of parliament, its eight senators in the upper house, as well as its 51 members in the Sindh provincial assembly.

The resignations will create a significant vacuum in parliament, if and when they are accepted, says the BBC Shahzeb Jillani in Karachi.

He says this could lead to a major by-election, which the government of PM Nawaz Sharif is keen to avoid.

What is MQM?

Image copyright AFP

1984: Founded as the party of Urdu-speakers who migrated from India at the time of the 1947 partition, known as Muhajir

1988: Wins all seats in Karachi, becoming Pakistan's third largest party

1992: Party chief Altaf Hussain leaves country after an arrest warrant is issued in a murder case; army claims to have busted "torture cells" used by MQM activists to punish opponents

2004: Emerges as major ally of military ruler General Pervez Musharraf

2014: London police raid the home of Altaf Hussain, who still controls the party, and investigate claims of money laundering and murder