China said Thursday it had summoned diplomatic envoys from Thailand, Laos and Myanmar and asked them to speed up a probe into a raid on two Chinese cargo boats on the Mekong that killed 13 people.

The attack on October 5 is thought to have been carried out by a notorious gang in the "Golden Triangle" area known for drug smuggling. One body was found on a ship while the rest were retrieved from the river. All had gunshot wounds.

China's Vice Foreign Minister Song Tao on Thursday summoned the ambassadors from Laos and Myanmar and the Thai charge d'affaires over the raid on the cargo ships "Hua Ping" and "Yu Xing 8", the foreign ministry said in a statement.

Song told the envoys China wanted the three countries to "increase the pace of the investigation, find out the truth about the incident as soon as possible and promptly inform the Chinese side".

Song also asked the countries to guarantee the safety of Chinese shipping crews in the future.

The dead included women and a teenager, according to Sermsak Srisant, district chief of Chiang Saen in northern Thailand, near the borders with Laos and Myanmar.

He told AFP earlier this week that authorities believe the two boats were attacked by a drug group active in the Golden Triangle, adding that 920,000 amphetamine tablets were discovered onboard.

Sermsak said the gang could have hijacked the boats further north on the river, between Myanmar and Laos, and attempted to force the crew to carry illicit cargo, but that a shootout appeared to have broken out.

Drug kingpin Nor Kham, who is wanted by the Myanmar authorities, was believed to have been behind the attack, he said.

Also on Thursday, China sent patrol boats from Yunnan province sailing south along the Mekong to escort 164 stranded Chinese sailors and 28 cargo ships north from Thailand back home to China, Xinhua said.

China earlier suspended Chinese ships from plying the Mekong after the attack.

The two attacked Chinese vessels will remain in Thailand.

Twenty-nine family members of the 12 sailors who died in the attacks also set out for Thailand from the China-Laos border on Thursday, Xinhua said.

They are expected to identify the bodies and attend a memorial service upon arrival.

Each family of a "Hua Ping" sailor killed will get 133,300 yuan ($20,883) in compensation from China Continent Property and Casualty Insurance, Xinhua said.

The families of the five insured "Yu Xing 8" victims will get 100,000 ($15,666) each from People's Insurance.