The co-pilot of the helicopter that crashed outside Mexico City on Friday, killing Interior Minister Francisco Blake and all seven others on board, had told his brother the craft was faulty, a newspaper report said on Sunday.

My brother told me on Wednesday. That helicopter is not OK and it was failing on the way back from Colima, Hiram Fernando Escobar told El Universal newspaper of his conversation with brother Pedro Ramon Escobar.

The helicopter spent one day being repaired in the presidential hangar before flying again on Friday, he told the newspaper.

Mexico's Communications and Transportation Minister Dionisio Perez-Jacome told a news conference on Saturday the helicopter, made in 1984, had been serviced between November 4 and 6, and it had flown on November 9 and 10 without any reports of problems.

The Communications and Transportation Ministry said on Sunday it will give an update on the crash investigation in a news conference at 1300 in Mexico (1900 GMT).

Preliminary investigations into the crash suggest that the helicopter crashed into the hillside outside of Mexico's capital after running into thick fog.

The helicopter, transporting Blake to an event in Cuernavaca about 60 miles (100 km) south of Mexico City, encountered low-lying clouds. At that point, to seek better visibility the pilot diverted from the planned route but floundered in the fog.

Initial checks of the helicopter showed no damage from an explosion or fire, Perez-Jacome said. A more exhaustive investigation is under way.

Blake, 45, was the second interior minister under President Felipe Calderon to be killed in an air crash, which prompted some Mexicans to speculate on Twitter about the cause of his death.

As interior minister, Blake was responsible for helping Calderon in the country's fight against powerful drug cartels.

Separately, a poll published by Milenio newspaper on Sunday showed 36 percent of people surveyed in Michoacan state -- where there are state elections on Sunday -- believe the helicopter crashed as a result of an attack, while 43 percent believe it was an accident.

(Reporting by Elinor Comlay; Editing by Philip Barbara)