A powerful bomb attached to a motorcycle exploded near a vehicle carrying police officers in restive southwest Pakistan on Friday, killing seven people, including five nearby children, officials said.

Local police chief Fateh Mohammad said the attack occurred in Mastung, a district in Balochistan province. He said a motorized rickshaw carrying schoolchildren was nearby when the bombing happened, resulting in the deaths of five children, a police officer and a passerby.

No one immediately claimed responsibility for the attack, but suspicion is likely to fall on separatist groups that have stepped up attacks on security forces and civilians in recent months.

Prime Minister Shehbaz Sharif and the chief minister of Balochistan, Sarfraz Bugti, both denounced the bombing and vowed to continue the war against insurgents until they are eliminated from the country.

Balochistan is the site of a long-running insurgency, with an array of separatist groups staging attacks mainly on security forces. The groups, including the Baloch Liberation Army, demand independence from the central government.

The BLA has also attacked foreigners. Last month, it claimed responsibility for a bombing that targeted Chinese nationals outside an airport in the southern city of Karachi, killing two workers from China and wounding eight people.

Thousands of Chinese workers are in Pakistan as part of Beijing’s multibillion-dollar Belt and Road Initiative, which is building major infrastructure projects.

Beijing has frequently demanded better security for its nationals in Pakistan.

China's ambassador to Pakistan, Jiang Zaidong, urged Pakistan at a seminar this week to take action against the insurgents responsible for “unacceptable” attacks on Chinese working on projects related to the China-Pakistan Economic Corridor, a sprawling package that includes road construction, power plants and agriculture.

Pakistan Foreign Ministry spokesperson Mumtaz Zahra Baloch on Thursday expressed her surprise over the ambassador's remarks, saying that Deputy Prime Minister Ishaq Dar, who also attended the seminar, had said “Pakistan is committed to providing full security to Chinese nationals, projects and institutions in Pakistan. Our commitment has been conveyed at the senior most levels of the Chinese government.”

She said Jiang's statement was “perplexing in view of the positive diplomatic traditions.”

One Pakistani hotel chain, Avari, said the government has instructed that transportation and airport transfers for Chinese guests must be arranged by the host or sponsor “via a bomb/bullet-proof vehicle” with security protocols.