The decision added drama to the major aerospace industry event, which was already under the shadow of last week's deadly crash of Air India's Boeing 787 Dreamliner.

Black walls were installed around the stands of five Israeli defence firms at the trade fair in Le Bourget, an airfield on the outskirts of Paris.

The booths displayed "offensive weapons" that could be used in Gaza -- in violation of agreements with Israeli authorities, a French government source told AFP.

The companies -- Israel Aerospace Industries (IAI), Rafael, Uvision, Elbit and Aeronautics -- make drones and guided bombs and missiles.

An Israeli exhibitor wrote a message in yellow chalk on one of the walls, saying the hidden defence systems "are protecting the state of Israel these days. The French government, in the name of discrimination is trying to hide them from you!"

French Prime Minister Francois Bayrou defended the decision during a Monday press conference at the air show.

"The French government's position was very simple: no offensive weapons at the arms exposition," he said.

"Defensive weapons were perfectly acceptable," he added.

- Conflicts loom large -

Bayrou cited the ongoing conflict in Gaza as the rationale behind the ban.

"Given the situation in Gaza... which is extremely serious from a humanitarian and security point of view, France was keen to make it clear that offensive weapons should not be present at this exposition," Bayrou said.

Israeli President Isaac Herzog said he was shocked by the "outrageous" closure of the pavilions and said the situation should be "immediately corrected".

"Israeli companies have signed contracts with the organisers... it's like creating an Israeli ghetto," he said on French television channel LCI.

The Israeli defence ministry said in a statement that the "outrageous and unprecedented decision reeks of policy-driven and commercial considerations".

"The French are hiding behind supposedly political considerations to exclude Israeli offensive weapons from an international exhibition -- weapons that compete with French industries," it said.

"This is particularly striking given Israeli technologies' impressive and precise performance in Iran."

Israel launched surprise strikes on Iranian military and nuclear sites on Friday, killing top commanders and scientists, prompting Tehran to hit back with a barrage of missiles.

The presence of Israeli firms at Le Bourget, though smaller than in the past, was already a source of tension before the start of the Paris Air Show, because of the conflict in Gaza.

A French court last week rejected a bid by NGOs to ban Israeli companies from Le Bourget over concerns about "international crimes".

Local lawmakers from the Seine-Saint-Denis department hosting the event were absent during Bayrou's visit to the opening of the air show in protest over the Israeli presence.

"Never has the world been so disrupted and destabilised," Bayrou said earlier at a roundtable event, urging nations to tackle challenges "together, not against each other".

- Boeing 'focus on supporting customers' -

The row over Israel cast a shadow over a trade fair that is usually dominated by displays of the aerospace industry's latest flying wonders, and big orders for plane makers Airbus and Boeing.

Airbus announced an order of 30 single-aisle A320neo jets and 10 A350F freighters by Saudi aircraft leasing firm AviLease.

The European manufacturer also said Riyadh Air was buying 25 long-range, wide-body A350-1000 jets.

But Boeing chief executive Kelly Ortberg last week cancelled plans to attend the biennial event, to focus on the investigation of the Air India crash.

"Our focus is on supporting our customers, rather than announcing orders at this air show," a Boeing spokeswoman told AFP on Monday.

The London-bound Dreamliner crashed shortly after take-off in the western Indian city of Ahmedabad, killing 241 passengers and crew and another 38 on the ground. One passenger survived.

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