The committee looking into the State Audit Office (SAO) building collapse will explore multiple factors, including subpar materials and building design, says Interior Minister Anutin Charnvirakul.
Mr Anutin, who is also the director of the National Disaster Prevention and Mitigation Command, recently met the committee to assess progress of the investigation.
He said on March 30 that the committee would take seven days to come up with preliminary findings.
Following the recent meeting, Mr Anutin said that while the one-week timeline allowed for the initial cause to be identified, ongoing recovery and rescue operations at the site had hampered the full access needed for collecting material samples.
He said the preliminary investigation pointed to issues related to the building's design, which will now undergo deeper analysis.
Mr Anutin said buildings in Thailand must meet high seismic and vibration standards incorporated in their structural design, so they can withstand earthquakes such as those originating from Myanmar.
A detailed engineering analysis is underway and may take months to complete, he said.
Drawing on the panel's work, the minister also raised concerns about the SAO building's lift shaft, which was located at the rear rather than the centre of the construction site.
He said the location may have caused torsion forces. Whether the safety factor used in the design was adequate will need to be reviewed, he said.
Meanwhile, the Chinese Embassy responded to public concerns over the involvement of China Railway No 10 (Thailand), a contractor in the SAO building's construction.
Some critics suspect sub-standard materials may have been used in the work.
The embassy, while affirming its support for a thorough and fair probe into the firm, rejects "blanket, false accusations against Chinese companies operating in Thailand".
Deputy government spokesman Karom Phonphonklang said 59 provinces were affected by the recent earthquake, with 179 businesses feeling some impact.
He said the collapse has so far left 15 people dead and nine others injured, with 79 others still missing.
