QUETTA, Pakistan—In the early hours of April 18, a group of militants in southwestern Pakistan blocked the coastal highway that connects the port of Gwadar, near the Iranian border, to Karachi farther east. The militants stopped six buses near a mountain pass and checked the identity cards of all the passengers. They singled out 14 members of Pakistan’s armed forces, and then executed them all.

People across Pakistan woke up to the disturbing news the next morning. Hours later, a coalition of three Baloch separatist groups, known as Baloch Raaji Aajoi Sangar, or BRAS, claimed responsibility for the attack. A coalition spokesman said that such violence would continue until China ceased all activity in southern Pakistan. The same group had previously claimed responsibility for an attack on the Chinese Consulate in Karachi and a bus of Chinese engineers in the town of Dalbandin, north of Gwadar.

Just last week, one of the groups in that coalition, the Baloch Liberation Army, or BLA, claimed responsibility for a deadly attack by heavily armed gunmen on a luxury hotel in Gwadar. “Our fighters have carried out this attack on Chinese and other foreign investors who were staying in [the] hotel,” the BLA’s spokesman told Al Jazeera. In another statement, the group added: “Expect more attacks China and Pakistan.”

Baloch insurgents are fiercely opposed to the Chinese presence in Gwadar, where major projects, including a new modern port, are underway as part of a costly building spree to upgrade infrastructure across Pakistan, costing tens of billions of dollars and all funded by Beijing under its mammoth Belt and Road Initiative. But to Baloch insurgents and separatists, all that investment and development is really about looting and plundering natural resources in Balochistan province, which they want to declare independent from Pakistan.

The repeated attacks by Baloch insurgents have limited the movement of Chinese workers in Balochistan and delayed construction of projects due to security concerns. Following last week’s hotel attack in Gwadar, Pakistan’s prime minister, Imran Khan, said, “Such attempts especially in Balochistan are an effort to sabotage our economic projects and prosperity.” The recent violence has again reignited the fears of security threats for Chinese interests in southern Pakistan. April’s bus attack, in particular, brought in a new angle: the apparent use of nearby Iranian territory by Baloch insurgents to mount their attack.

In the aftermath of the April bus attack, the Pakistani Foreign Ministry alleged that BRAS has training camps based in Iran, which it uses to attack Pakistan. The ministry wrote a formal letter of protest to the Iranian government and demanded it take action against what it called BRAS sanctuaries in Iran.

In the past, the Iranian government has been bitterly opposed to Baloch insurgents and separatist forces, since it faces its own Baloch insurgency in southeastern Iran, led by Sunni Baloch militants. But now Tehran seems to have shifted its policy due to rifts in its relations with Pakistan. Iran fears a growing Saudi presence in southern Pakistan, after Saudi Arabia recently signed an agreement to build a $10 billion oil refinery in Gwadar and invest in what had been a China-backed development program. Tehran worries that Pakistan is allowing Saudi Arabia to use Gwadar as a launching pad to destabilize Iran, by stoking the long-running Baloch insurgency. Just as Pakistan accuses Iran of harboring Baloch separatists like BRAS, Iran blames Pakistan for giving sanctuary to militant Sunni Baloch groups such as Jaish al-Adl that have attacked Iranian security forces in Iran’s Sistan and Balochistan province.