France has taken the European Union into uncharted territory by obliging the other 27 member states to come to its defence following the terrorist atrocities in Paris.

Invoking article 42.7, a never used clause of the EU treaty triggering mutual defence among the 28 member states, Paris admitted it was struggling to cope with its foreign military commitments while beefing up security at home in the wake of the attacks, and asked the rest of Europe to come to its assistance.

The request was supported unanimously in what Jean-Yves Le Drian, the French defence minister, described as an emotional and highly charged meeting of EU defence ministers in Brussels.

As a result of the train attacks in Spain in 2004, the EU inserted mutual defence measures into the Lisbon treaty similar to the Nato alliance’s article five, which obliges all member countries to come to the defence of one of their number if attacked.

As the EU does not have an army, the French will now conduct a set of bilateral negotiations with other EU states on what kind of military help might be available.

Article 42.7 stipulates that “if a member state is the victim of armed aggression on its territory, the other member states shall have towards it an obligation of aid and assistance by all the means in their power, in accordance with article 51 of the United Nations charter”.

However, the article adds: “This shall not prejudice the specific character of the security and defence policy of certain member states.”

The latter sentence means that the neutrality of countries such as Ireland, Austria, and Sweden cannot be impugned, while the emphasis on help from “member states” means that the defence arrangements are agreed between national governments in the EU without the involvement of the institutions in Brussels such as the European commission or the European parliament. This leaves France free to strike deals with other governments without any interference from Brussels.

By contrast, article 222 of the treaty, eschewed in this instance by the French, says that “the union and its member states shall act jointly in a spirit of solidarity if a member state is the object of a terrorist attack or the victim of a natural or man-made disaster. The union shall mobilise all the instruments at its disposal, including the military resources made available by the member states.”

This would hand a major role to the European commission, which Paris has opted to avoid.

The British government said it stood ready to assist the French. The German defence minister, Ursula von der Leyen, said that the French invocation of the mutual defence clause meant only that there was “a basis for consultation”.

A priority is likely to be an attempt at greater sharing of intelligence among EU states to try to counter terrorism, amid growing evidence that failure to act on intelligence by the French and Belgian security services may have contributed to the Paris attacks.

“We need greater intelligence sharing,” said an ambassador to the EU.

The issue is likely to come up on Friday at an emergency meeting in Brussels of EU interior ministers.

Reinforcing the external borders of the EU is another area where the pledges might be applied, with increasing talk of military elements being added to police operations on the EU’s frontiers.

But Paris also appeared to be asking its EU partners for some relief from its foreign military commitments, including participation in UN missions in Africa and Lebanon as well as its involvement in the bombing campaign against Islamic State in Syria and Iraq.

Le Drian admitted that France was overstretched. “France can’t do everything. It can’t act alone,” he said. “Every country said, I am going to help you. That can take different forms. There are many types of assistance possible, whether in the Middle Eastern arena or elsewhere.

“How is this going to work?” said Le Drian. “It may be by cooperating with French interventions in Syria, in Iraq, it may be in support of France in other operations.”

Attending the EU defence meeting, the Nato secretary general, Jens Stoltenberg, said Paris had not tabled any parallel request to trigger article five.

“It’s a political act, a political message,” said Federica Mogherini, the EU’s foreign and security policy coordinator. Each member state would contribute to helping France in line with their capabilities and foreign policies, she added. The details would be developed in a set of bilateral talks between national governments and France.

“The prime minister has been clear that we will do whatever we can to help the French government at this time, and that we need to work together to defeat these terrorists,” said a UK government spokesman.

“We have been in constant contact with the French authorities since Friday. This is about a French request for bilateral assistance from other EU member states. We understand and support the French decision, and we stand ready to consider any French request for assistance.”

EU positions on Syria were shifting as a result of the Paris attacks, senior diplomats said. Britain, Germany, Italy and Spain are now said to support concentrating military efforts on eradicating Isis and being less insistent for the time being on bringing down the Syrian regime.

France, which has consistently taken the most hawkish line on the regime of President Bashar al-Assad, was not diluting its position, the diplomats said, while tiny Luxembourg, currently chairing the EU, takes the toughest line of all, arguing that Assad should be deposed by military means.