Eight people have been arrested by Vietnamese police in connection with the 39 migrants who were found dead in a lorry in Essex.
They were held on Sunday on suspicion of organising people smuggling overseas.
The 31 men and eight women who were discovered in the back of the refrigerated truck in Grays are thought to have been Vietnamese.
A spokeswoman for the country's Ministry of Foreign Affairs called the incident a "serious humanitarian tragedy".
On Saturday, a remembrance service for the victims was held at the Church of the Holy Name and Our Lady of the Sacred Heart in Bow, east London, which has a large Vietnamese congregation.
The Rev Simon Nguyen told the PA news agency that the church has assisted with the investigation into the tragedy, including working with the police.
So far two people have been charged.
Essex Police have started extradition proceedings to bring 22-year-old Eamonn Harrison from Ireland to the UK.
Harrison, of Newry in Co Down, appeared at Dublin High Court on Friday charged with 39 counts of manslaughter, along with human trafficking and immigration offences, and was remanded in custody.
The driver of the lorry, Maurice 'Mo' Robinson (25), appeared at Chelmsford Magistrates Court charged with 39 counts of manslaughter, conspiracy to traffic people, conspiracy to assist unlawful immigration and money laundering.
Detectives have also urged Ronan Hughes (40) and his brother Christopher (34), said to have links with the road haulage and shipping industries, to hand themselves in.
The pair, from Armagh, are wanted on suspicion of manslaughter and human trafficking.
It is understood Ronan Hughes spoke to police shortly after Robinson was arrested.
Three other people arrested - two men aged 38 and 46 and a 38-year-old woman - have been released on bail.
The investigation in Vietnam was prompted when 10 families from Nghen Town, Thien Loc, Vinh Loc and Thanh Loc contacted authorities to say they had lost contact with their relatives.
It is still not known how the victims, who police in England initially believed were Chinese nationals, entered the lorry trailer before it travelled from Zeebrugge in Belgium to Purfleet in Essex.
The discovery of the bodies in a refrigerated truck on an industrial estate near London has shone a spotlight on the illicit trade that sends the poor of Asia, Africa and the Middle East on perilous journeys to the West.
It is understood the father of one of the dead found in Essex paid around £30,000 to people smugglers to make the desperate and dangerous journey to England.
The Vietnamese embassy in the UK had been working closely with the British authorities to support families and help find the identities of the victims.