By Gul Yousafzai

QUETTA, Pakistan (Reuters) - Pakistani forces killed three militants at the start of a crackdown on sectarian militant group in the southwestern province of Baluchistan, officials said on Thursday, following a spate of attacks targeting security forces.

The extremist Sunni Muslim group Lashkar-e-Jhangvi (LeJ), whose roots are in Punjab province, claimed responsibility for gunning down four policemen on Tuesday and four soldiers of the paramilitary Frontier Corps in the city of Quetta on Wednesday.

A spokesman for the paramilitary Frontier Corps said the government had decided to launch an armed operation against LeJ at a late night meeting on Wednesday.

"Three terrorists belonging to LeJ have been killed in an armed clash with Frontier Corps and intelligence personnel," said Khan Wasey, the spokesman for the paramilitary force.

He said the killings took place during a search operation in the early hours of Thursday.

Last year, police killed the leader of the LeJ, Malik Ishaq, signaling a shift in the Pakistani government's strategy for dealing with the group.

Baluchistan chief minister Sananullah Zehri condemned the killing of the policemen and soldiers and said "strict actions would be launched against terrorists and their supporters".

Baluchistan is Pakistan's poorest and least developed province and has suffered a long-running separatist violence.

Ethnic Baluch activists and human rights groups accuse the military of carrying out a campaign of kidnapping, torture and extrajudicial killing against suspected separatists, and a security measures have severely limited freedom of movement in the province.

Pakistan and China are developing multi-billion-dollar energy and infrastructure projects in the sparsely populated region as part of a plan to create a corridor stretching from the Arabian Sea to China's Xinjiang region.

(Writing by Mehreen Zahra-Malik; Editing by Simon Cameron-Moore)