The French foreign ministry said it regretted "that Lebanese leaders have not yet managed to keep the commitments made on September 1" when they pledged to form a Cabinet within two weeks.
"We call on them to find an agreement without delay for the formation of a new government by Mustapha Adib," added the statement.
Prime minister-designate Adib has been unable to form a new Cabinet, which is required to unlock billions of dollars in foreign aid, because of disagreements between political parties.
Adib's efforts have been effectively blocked by the two main Shiite groups in Lebanon's usual power-sharing arrangement — Amal and Hizbollah.
Observers have said their insistence on keeping the finance ministry is linked to recent US sanctions against a former minister from Amal, as well as Hizbollah-linked businesses.
An explosion of hundreds of tonnes of ammonium nitrate at the Beirut port on August 4 killed more than 190 people, wounded thousands and prompted the government to quit.
French President Emmanuel Macron, who has visited Lebanon twice since the disaster, has set himself up as a broker between political factions in the country, urging them to pass reforms required to get the tanking economy back on track.