PARIS -- France is bolstering its security on land and at sea in the face of attack threats, and has started airdropping armed military officers from a helicopter onto ferries crossing the English Channel.

Other sea routes, including across the Mediterranean, are also being secured, Lieut. Pierre Joachim Antona, spokesman for the local maritime authority in Cherbourg said Wednesday.

Interior Minister Bernard Cazeneuve reiterated the need for increased security on land, especially in the summer season which is at its height in August when numerous festivals are held. Some have been cancelled, including major events in Marseille and Nice.

"Our objective is to ensure and guarantee a high-level presence and a high level of security during the summer period," Cazeneuve said after a Defence Council meeting, a regular event since the July 14 truck attack in Nice that killed 84 people who were celebrating France's national day. Less than two weeks later, two extremists murdered a priest in his Normandy church during Mass.

The minister said that 12,500 reservists have joined police forces to support extra security measures. The 10,000-strong Sentinel Operation of soldiers will continue to patrol French streets and sensitive sites like airports and train stations.

On Monday afternoon, hundreds of passengers aboard the Mont-Saint-Michel ferry between Britain and France may have been stunned to see a French military helicopter airdrop a group of armed and fully-uniformed maritime gendarmes onto their vessel for the first such "securing and protecting mission" in the English Channel.

Antona, of the Maritime Prefecture in Cherbourg, France, said the airdrop took place when the ferry entered French waters from the southern English port of Portsmouth on its way to the Normandy port of Caen.

The missions only involve French ferries sailing in French waters until an agreement under discussion with British authorities is signed, "possibly within weeks," Antona said. Such an agreement would allow French military officers to board ferries directly from English ports, the military spokesman said.

Missions are expected to be carried out "randomly and regularly" on passenger ferries between France and Britain "to deter, observe, give intelligence and possibly intervene if needed," Antona said.

Orders to secure such vessels, which are seen as possible targets for terrorists, went out to all maritime prefectures in France on Aug. 1, officials have said.

The Maritime Prefecture in Toulon in southern France said securing operations there began even earlier, but spokeswoman Sarah Cottin refused to provide routes, destinations or operational techniques, citing security.

Ferries travel from French continental ports to the Mediterranean island of Corsica and to North African countries like Algeria and Tunisia.

Meanwhile, Cazeneuve, the interior minister, promised to maintain as many summer events as possible.

"When the conditions are not met to ensure maximum security, of course local governments can make a decision to cancel some events," Cazeneuve told reporters.

Several cities and towns have downsized or cancelled some summer festivities following the attacks, including fireworks displays in Marseille, Avignon or La Baule on the Atlantic coast. Marseille's authorities also called off a major air show which was expected to draw 100,000 spectators next week.

In Paris, a car-free day on the city's famed Champs-Elysees Avenue scheduled on Aug. 7 and a street basketball tournament which was to feature NBA star Kobe Bryant have been called off.

Free film showings that usually take place outdoors all summer have been authorized only if they are moved indoors.

The popular Paris Plages, a month-long beach event along the Seine River, has been maintained with concrete barriers added around the area to guard against a repeat of the attack in Nice.

In that mourning city on the French Riviera, the "Prom' Party" that usually turns Nice's seafront into a dance floor in the second half of August has been cancelled.