Police said in a statement: "Due to concerns around items found at the address ... officers have extended the cordon surrounding the property.
"Neighbours are being temporarily evacuated."
Members of the media were also moved back around 200 yards.
Saad al-Hilli, 50, was killed in his car alongside his dentist wife, Iqbal, on Wednesday while the couple's four-year-old daughter Zeena lay undiscovered under her mother's corpse for eight hours and her sister Zainab narrowly escaped death after being shot and beaten.
Meanwhile, French police have confirmed that the third victim was Mr al-Hilli's 74-year old mother-in-law, but have not named her.
Sylvain Mollier, 45, a French cyclist who apparently stumbled across the attack, was also shot and killed.
Attention on the property intensified as French police waited to question seven-year-old Zainab, who has regained consciousness following the attack that left her parents dead.
Zainab's younger sister Zeena, four, flew back to Britain with carers yesterday.
Soon after the cordon was extended, a Royal Logistic Corps bomb disposal truck arrived.
Police are examining all aspects of Mr al-Hilli's life to try to find a motive for the murders. They have also been speaking with his brother, Zaid Hilli.
Investigators have disclosed that Mr al-Hilli's brother has approached UK police to deny any feud with his sibling over a family inheritance.
Police have yet to speak to Zainab, who was shot and beaten during the ordeal and is seen as a key witness.
She remains under sedation after coming out of a medically-induced coma.
French public prosecutor Eric Maillaud said the child will be interviewed as soon as doctors allow it.
Her sister returned to the UK after an aunt and uncle travelled to France over the weekend alongside a British social worker and police family liaison officers.
The youngster is now under the care of the authorities and the social services, but Mr Maillaud revealed he did not know where she was going to stay.