Bangladesh authorities investigating this month's deadly terror attack at a Dhaka cafe are now exploring potential foreign links, including one man who had been living in Australia.

Key points: Islamic State claim responsibility for cafe attack

Islamic State claim responsibility for cafe attack Authorities examining list of potential militants including suspected IS recruiters

Authorities examining list of potential militants including suspected IS recruiters Attackers identified as sons of well-to-do families

The whereabouts of the man, named as Abu Terek Mohammad Tajuddin Kausar, are now unknown, but the acknowledgement of possible foreign involvement marks a major development in Bangladesh, which had consistently rejected Islamic State's claim of responsibility.

Bangladesh authorities said they were tracking Mr Tajuddin, who is originally from Lakshmipur, south of Dhaka, and has spent time living in Australia, but said they were currently unsure of his whereabouts.

The Australian Federal Police were contacted regarding Mr Tajuddin but a spokesperson said the AFP would not comment on intelligence matters.

Bangladesh authorities are examining a list of potential militants which also includes suspected IS recruiters.

Twenty-two people, 18 of them foreign nationals, were killed by five machete-wielding attackers at the Holey Artisan Bakery in Dhaka's upmarket Gulshan district on July 1 — a major escalation in Bangladesh's Islamist violence.

Until recent days Bangladeshi authorities had blamed homegrown groups for the attack.

However, after the attackers were identified as the sons of well-to-do families, more parents whose children were missing, presumed radicalised, began to come forward.

"It was shocking, we never expected it to be like that," former military chief, retired air commodore Ishfaq Ilahi said.

"There is a new realisation, that we can't just hide this under the carpet."

'Credible evidence' of links to Islamic State

Police outside the scene of the Dhaka cafe massacre ( Facebook: Shaheen Mollah )

Among those identified as "missing" are one naval officer who told his parents via Facebook he had gone to Iraq to wage jihad.

Five members of another family are known to have travelled to Syria which has led to an acknowledgement from police that IS may be involved.

"Those who carried out the Gulshan attack were all Bangladeshis, but I don't rule out their possible foreign links," Dhaka police commissioner Asaduzzaman Mia was quoted as telling reporters several days ago.

Bangladeshi security consultant Shahab Enam Khan said there was now little doubt that means IS was involved.

"We are now discovering, and there is now credible evidence that people from here had linkages with ISIS," he said.

"This is significant for sure, because the government actually ruled out the possibility of ISIS for some time. But now that there is new evidence … these particular linkages between the missing boys and the connection with Syria, well there is a possibility of some sort of linkages between the homegrown terrorists as well as with ISIS."

Mr Khan said alongside Mr Tajuddin, Bangladesh was also searching for two others who had spent time in Western countries.

"One from Canada, and the other one studied in Japan, so you now can see that there is a growing trend and a credible trend that is coming up — that we have a strong transnational linkage," he said.