* Security forces make their way into hospital
* Dozens of hostage released, government says
* Baluchistan plagued by sectarian violence, separatist insurgency (Recasts with end of siege, updates casualties)
By Gul Yousafzai
QUETTA, Pakistan, June 15 (Reuters) - Militants in a volatile region of western Pakistan bombed a bus carrying women students on Saturday and then seized part of the hospital where survivors were taken, in the first major security test for the new prime minister, Nawaz Sharif.
At least 22 people were killed in a day of violence that started with an apparent separatist attack that destroyed a summer retreat once used by the nation's founder Muhammad Ali Jinnah in the hills of Baluchistan province.
A policeman lost his life in the attack on a popular symbol of Pakistan's history, which was gutted by fire after several small bombs were detonated.
"Baluchistan is part of Pakistan and we will not leave our people alone in a time of tragedy," Information Minister Pervaiz Rashid told reporters in a news conference.
The first attack was quickly followed by a bus bomb on a university campus in Baluchistan's capital Quetta that killed at least 14 women students.
The injured were taken to the city's Bolan Medical Complex, where an ambush by a suicide bomber and an ensuing firefight with security forces killed at least eight more people.
The government said the Quetta attacks were not connected with the earlier blasts at the hill retreat.
The violence brought an abrupt end to a period of relative calm after Pakistan's first ever transition between elected civilian governments, which brought Sharif to office for the third time, and highlighted the deep fissures in the nation he must govern.
As well as the fragile security situation, Sharif has inherited a severe energy crisis and a weak economy. He must also manage a complex relationship with the United States, including nationwide anger at U.S. drone attacks.
At least 36 were injured in Saturday's violence. Four militants including two suicide bombers were among the dead at the hospital, where security forces moved from room to room freeing trapped patients and doctors, the government said.
Four nurses were also reported dead.
By nightfall, Interior Minister Chaudhry Nisar Ali Khan said the hospital siege was over, with one suspect captured. Four members of the security forces were confirmed dead.
The new chief minister in Baluchistan, an ally of Sharif's, last week vowed to work towards talks to end a long running war with separatist guerrillas in resource-rich Baluchistan.
In addition to the separatist movement, Quetta is home to much sectarian violence, much of it targeting the Hazara ethnic minority, who are Shi'ite Muslims in a largely Sunni country.
It was not immediately clear who was responsible for the bus and hospital attacks, or whether they were aimed at the Hazaras.
City police chief Mir Zubair Mehmood told Reuters that the students on the bus were from various ethnic groups, including Hazaras, targets of a series of bombings this year. Another police official said the hospital blast seemed to be aimed at government officials who had rushed to the scene.
Saturday's attack was the biggest since bombings in the city at the start of the year killed almost 200 people, briefly drawing global attention to a growing campaign of victimisation of the Hazaras by sectarian militants.
Their 500,000-strong community in Quetta has been subjected to a campaign of shootings and bombings by Lashkar-e-Jhangvi (LEJ), a militant group dedicated to attacking the Shi'ite minority.
The attack on Jinnah's hill retreat in the town of Ziarat was claimed by the separatist Baluchistan Liberation Army, Baluchistan's top policeman Mushtaq Sukhera said. Reuters was unable to contact the insurgents to verify that claim.
Jinnah stayed in the woodland Quaid Azam Residency as he tried to recover from a lung disease in 1948, a year after his successful campaign to separate Pakistan from India. He died in Karachi soon after. The building is a national heritage site.
Several men surrounded the house in the early hours of the morning before detonating several bombs, local police and an eyewitness said.
A policeman died and the ensuing blaze tore through the two-storey wooden-clad building, destroying historical relics.
Baluchistan is laden with copper and gold deposits that are largely unexploited. It also supplies much of the natural gas feeding Pakistan's lifeline textile industry in eastern Punjab province, and is home to a deepwater port at Gwadar.
Chief Minister Abdul Malik last week called on security forces, who deny wrongdoing, to end a campaign of enforced disappearances to support his hopes of kindling dialogue. (Reporting by Gul Yousafzai, additional reporting by Syed Raza Hassan; Writing by Frank Jack Daniel; Editing by Michael Perry and Ron Popeski)