The United Nations and Pakistan have strongly condemned a series of terrorist attacks that claimed more than 50 lives in the country's southwestern Balochistan Province on Monday.

"The secretary-general stresses that attacks against civilians are unacceptable," said Stephane Dujarric, spokesperson for UN chief Antonio Guterres, at a daily briefing on the same day.

Guterres extended his deepest condolences to the families of the victims and called on the Pakistani government to conduct an investigation and ensure that those responsible are held accountable, he added.

At least 53 people, including 10 security forces soldiers and four law enforcement personnel, were killed by militants in Pakistan's largest province by land on Monday, according to Pakistan military authorities.

President Asif Ali Zardari said the "brutal killing of innocent people was the killing of the entire humanity" and demanded that the culprits be brought to justice, Radio Pakistan reported.

Prime Minister Shehbaz Sharif also strongly condemned the attacks, demanding an immediate probe to bring the perpetrators to justice. "The nation stood by the security forces in the war against terrorism … Terrorists' nefarious designs to spoil the country's peace would never succeed," Sharif said.

China voiced strong condemnation of terrorist attacks in Pakistan and expressed deep condolences to the victims on Tuesday.

Maintaining unity

Foreign Ministry spokesman Lin Jian told a daily briefing that China firmly opposes all forms of terrorism and will continue to firmly support Pakistan in advancing counterterrorism operations, maintaining social unity and stability and protecting people's safety.

Attacks on police stations, other law enforcement buildings and innocent civilians were launched shortly before midnight on Monday, continuing into the morning with gunfire, grenades, suicide bombings and bomb attacks.

Terrorists launched attacks in various areas of Balochistan, including Musa Khel, Kalat and Las Bela districts, according to a statement from the Inter Services Public Relations Pakistan, or ISPR, the media arm of the Pakistani military.

The largest attack in Musa Khel saw 23 people killed at close range after their vehicles were stopped, the district's Assistant Commissioner Najeeb Kakar said.

Terrorists blocked the highway connecting Balochistan with the eastern Punjab Province in Musa Khel, stopping buses and trucks and checking the identities of passengers before shooting them. Most of the victims were from southern Punjab.

The banned Balochistan Liberation Army, or BLA, reportedly claimed responsibility for the offensive in a statement emailed to some local journalists.

The ISPR reported that 21 terrorists were killed in tense fighting during a clearance operation conducted by security forces after the attacks.

Clearance operations are ongoing and the perpetrators and facilitators of heinous acts targeting innocent civilians will be brought to justice, the ISPR added.

"These attacks are a well thought-out plan to create anarchy in Pakistan," Interior Minister Mohsin Naqvi said in a statement on Monday.

The ISPR noted that the terrorists attempted to engage in numerous attacks in Balochistan aimed at disrupting the peaceful environment and development of the province by targeting mainly innocent civilians.

The Pakistani military said security forces and law enforcement agencies remained determined to thwart attempts at sabotaging peace, stability and progress in Balochistan.

Xinhua contributed to this story.