The Defence Cooperation Agreement (DCA) is a major step for a nation that in March ended two centuries of military non-alliance to join NATO.

Signed by Stockholm and Washington in December, the deal gives the US access to 17 military bases and training areas in Sweden, and allows the storage of weapons, military equipment and ammunition.

The agreement was approved by a broad majority in parliament following an almost five-hour debate, with 266 MPs voting in favour and 37 against, while 46 were absent.

The main opponents, the Left and Green parties, had argued that the agreement ought to state outright that the Scandinavian country would not allow nuclear weapons on its territory.

"We want to see legislation that bans nuclear weapons from being brought onto Swedish soil," Green Party MP Emma Berginger told parliament during Tuesday's debate.

"Unfortunately, the government has chosen to sign an agreement that doesn't close the door to nuclear weapons, and therefore the Green Party is going to vote no to this agreement," she told said during the debate.

Greens leader Daniel Hellden had argued Monday that the agreement made Sweden "a target for nuclear weapons" since "we're going to have 17 bases where the Americans can store (military) materiel".

Prime Minister Ulf Kristersson's centre-right minority government, propped up by the far-right Sweden Democrats, has said the deal respects Swedish sovereignty.

"It is very clear that Sweden is a sovereign nation, and there is no other country that can force Sweden to have nuclear weapons on Swedish soil," Defence Minister Pal Jonson insisted.

- 'Naive' -

The Left and Green parties, which also voted against Sweden's NATO membership, together hold just 42 seats in parliament, which was not enough to block the agreement's adoption on their own.

The Swedish Peace and Arbitration Association, one of the biggest critics of the move, said two successive Swedish governments insisted during the NATO application process that Sweden would have the same stance on nuclear weapons as neighbouring Denmark and Norway.

"But unlike Norway's and Denmark's DCA agreements, there is no clause in Sweden's agreement against nuclear weapons being brought into or placed in Sweden," the association's head Kerstin Bergea wrote in an op-ed.

In addition, Finland, which joined NATO in April 2023, "has a national law prohibiting nuclear weapons on Finnish territory and Finland's DCA agreement refers to this law".

A similar Swedish clause would "strengthen the Nordic region and contribute to a joint de-escalation vis-a-vis Russian nuclear weapons", Bergea said.

- Nukes in wartime? -

Sweden's prime minister made headlines last month when he opened the door for the possibility of nuclear weapons in the country during wartime.

"In a war situation it's a completely different matter, (it) would depend entirely on what would happen," Kristersson told public radio broadcaster SR.

Two Left Party MPs said in an op-ed on Sunday: "That's an incredible statement and is totally the opposite of what the Swedish people think and what Sweden has long stood for."

Bergea questioned whether Sweden would be able to put a brake on the United States.

"An agreement based solely on confidence is not enough in important matters such as these," she said.

Jonson, the defence minister, has said Sweden needed to strengthen its international cooperation "to defend our freedom and democracy".

"With the DCA, Sweden can receive early, swift and effective military support from the United States in a deteriorating security situation," he said last month.

"The agreement acts as a deterrent and is stabilising. It reduces the risk of war breaking out and makes Sweden safer," Jonson said.