Authorities in Pakistan have detained 13 men in connection with a car bombing that killed three Chinese engineers Monday in the southwest of the country.

Police officials in the remote coastal town of Gwadar say the suspects are being interrogated at an undisclosed location, but they refuse to give more details.

According to eyewitnesses, an explosive-laden car was blown up by remote control near a bus that was driving 12 Chinese engineers to work Monday. The attack instantly killed three of the Chinese, while nine others were wounded, four of them seriously. Their Pakistani driver and security guard were also injured.

More than 300 Chinese nationals are helping Pakistan build a deepwater port on the Arabian Sea in southwestern Baluchistan Province, bordering Iran.

A spokesman for the communications ministry, Iftikhar Rasheed, dismisses suggestions that poor security for the Chinese workers led to the attack.

"Maximum possible security measures were taken by the Baluchistan government, and they [security officials] are going to beef it up further in view of this incident," he said. "Foolproof security can never be made."

President Pervez Musharraf has described the attack as "a barbaric act of terrorism" and has promised to punish those responsible.

No one has claimed responsibility for Monday's bombing, but initial suspicion fell on Islamic militants opposed to Pakistan's increasingly close ties with the West, and especially its support for the U.S. led war on terrorism.

The theory is that attacks like these might scare off foreign investors and foreigners living in Pakistan, driving a wedge between Pakistan and the non-Muslim world. These religious forces are blamed for a series of terror strikes in Pakistan in recent years.

But top Pakistani officials do not rule out the possibility of involvement by nationalists in Baluchistan who are opposed to the Chinese-funded port project in Gwadar.