QUETTA, Pakistan: Thousands of Pakistani Shi'ites furious over a sectarian bombing that killed 89 people protested on Monday, demanding that security forces protect them from hardline Sunni groups.

The attack, near a street market in the southwestern city of Quetta on Saturday, highlighted the government's failure to crack down on militancy in nuclear-armed Pakistan just a few months before a general election is due.

Lashkar-e-Jhangvi (LeJ), seen as the most ruthless Sunni sectarian group, claimed responsibility for the latest bombing, just as they did for another bombing that killed nearly 100 people in the same city last month.

While the Taliban and al Qaeda remain a major source of instability, Sunni sectarian militants, who regard Shi'ites as non-Muslims, have emerged as another significant security threat.

Shi'ite frustrations with waves of attacks on them have reached boiling point, piling pressure on Pakistani leaders ahead of elections expected within a few months.

The government is already under fire for failing to tackle a host of other problems, from power cuts and corruption to poverty.

In Quetta, some ethnic Shi'ite Hazaras are refusing to bury their dead until the army goes after the LeJ.

Around 4,000 men, women and children placed 71 bodies beside a Shi'ite place of worship. Muslim tradition requires that bodies are buried as soon as possible, and leaving them above ground is a potent expression of grief and pain.

Some coffins contained three or four bags of remains, with photographs of the dead on top. Grown men wept beside a hand-written list of victims hanging on a wall.

Protesters chanted "stop killing Shi'ites".

"We stand firm for our demands of handing over the city to the army and carrying out a targeted operation against terrorists and their supporters," said Syed Muhammad Hadi, spokesman for an alliance of Shi'ite groups.

"We will not bury the bodies unless our demands are met."

The paramilitary Frontier Corps is largely responsible for security in Baluchistan province, of which Quetta is the capital, but Shi'ites say it is unable or unwilling to protect them.

The roughly 500,000-strong Hazara people in Quetta, who speak a Persian dialect, have distinct features and are an easy target for Sunni hardliners.

The LeJ has stepped up suicide bombings and shootings in a bid to destabilise strategic U.S. ally Pakistan and install a Sunni theocracy, an echo of the strategy that al Qaeda pursued to try and trigger a civil war in Iraq several years ago.

On Monday, Pakistanis demonstrated in other major cities including the capital Islamabad and Lahore, where Shi'ite activists put up lights along roads and passed out water during a sit in.

"Installation of lights and other arrangements indicate that we are ready to stay here till the government meets our demands and make necessary measures to stop Shia genocide in Pakistan," said Ammar Yasir, a local Shi'ite leader.

The city's lawyers staged a strike in solidarity with Shi'ites.

In Karachi, a strike to protest against the Quetta bloodshed brought Pakistan's commercial hub to a standstill.

Authorities boosted security as protesters blocked roads, disrupted rail services to other parts of the country and torched vehicles. Protesters clashed with police who stopped them entering the airport.