Separatist militant attacks on police stations, railway lines and highways in Pakistan's restive province of Balochistan, coupled with retaliatory operations by security forces, killed more than 60 people, officials said on Monday.

The most widespread assault by ethnic insurgents in years forms part of a decades-long effort to win secession of the resource-rich south-western province, home to major China-led projects such as a strategic port and a gold and copper mine.

"These attacks are a well-thought-out plan to create anarchy in Pakistan," Interior Minister Mohsin Naqvi said in a statement, adding that security forces had killed 12 militants in operations after the attacks on Sunday and Monday.

Pakistan's military said 14 soldiers and police, and 21 militants, were killed in fighting after the largest of the attacks, which targeted vehicles from buses to goods trucks on a major highway.

It was not immediately clear whether that included the 12 militants the interior ministry confirmed dead.

Local officials said at least 23 passengers were killed in the attack, with 35 vehicles set ablaze.

Rail traffic with Quetta was suspended following blasts on a rail bridge linking the provincial capital to the rest of Pakistan, as well as on a rail link to neighbouring Iran, railways official Muhammad Kashif said.

Police said they had found six unidentified bodies near the site of the attack on the railway bridge.

In a separate attack early on Monday, gunmen killed six security personnel, three civilians and a tribal elder in Qalat district in Baluchistan, authorities said.

Gunmen also attacked a police station in Mastung district in Baluchistan, but there were no reported casualties.

In separate statements, President Asif Ali Zardari and Interior Minister Mohsin Naqvi called the attack in Musakhail "barbaric" and vowed that those who were behind it would not escape justice.

Later, Mr Naqvi also condemned the killings in Qalat.

The attack in Musakhail came hours after the outlawed Baluch Liberation Army separatist group warned people to stay away from highways as it launched attacks on security forces in various parts of the province.

In a statement, the Balochistan Liberation Army (BLA) group said its fighters targeted military personnel travelling in civilian clothes, who were shot after being identified.

However, Pakistan's interior ministry said the dead were innocent citizens.

Separatists often ask people for their ID cards and then abduct or kill those who come from Punjab or other provinces.

In May, gunmen fatally shot seven barbers in Gwadar, a port city in Baluchistan.

In April, separatists killed nine people after abducting them from a bus on a highway in Baluchistan, and the attackers also killed two people and injured six in another car they forced to stop.

The BLA also claimed responsibility for those attacks at the time.

Syed Muhammad Ali, an Islamabad-based security analyst, said the latest killings of non-Baloch people was an attempt by separatists to harm the province economically.

He told The Associated Press that such attacks were designed to economically weaken Balochistan, noting that "the weakening of Baluchistan means the weakening of Pakistan".

He said insurgent attacks could hamper development work being done in the province.

Separatists in Balochistan have often killed workers and others from the country's eastern Punjab region as part of a campaign to force them to leave the province, which for years has experienced a low-level insurgency.

Most previous killings have been blamed on the outlawed group and others demanding independence from the central government in Islamabad.

Islamic militants also have a presence in the province.

AP/Reuters