"We have reached an agreement with the US authorities for other procedures in the event of a threat," Swedish Civil Aviation Administration spokesman Per Froeberg said.
He explained that the Swedish agency had agreed with the Transportation Security Administration if a threat were issued against a Swedish flight, they would then discuss necessary security measures.
Cancelling the flight would be the most likely option, Froeberg said.
On Monday, US Homeland Security Secretary Tom Ridge issued an emergency directive that foreign carriers put armed police on flights where US officials deemed there was a terrorist risk.
The announcement came eight days after US officials heightened a nationwide attack alert, citing intelligence that al-Qaida network wanted to stage an even bigger strike than the 11 September 2001 attacks.
Pilots working for Scandinavian carrier SAS had opposed Washington's request, saying they did not want firearms in the cabin and that they preferred tight security on the ground. SAS management said it was in principle also opposed to armed guards on flights, but deferred the issue to police and civil aviation authorities in the three Scandinavian countries.
Britain's aircraft pilots' body also said on Wednesday it had reached an agreement with one airline on rules governing armed air marshals, but added it was still against taking guns onto planes.
"We remain opposed to the whole concept of bringing sky marshal guns on board an aircraft. This will not make flights more safe," said Jim McAuslan, general secretary of the British Airline Pilots' Association (BALPA) in a statement.
Few Air France flights were halted
on Christmas Eve due to threat
BALPA said it would cooperate with stepped-up security measures announced after six Air France flights between Paris and Los Angeles were cancelled last week amid "terror" fears.
"We have always said that if the government persists with its decision that sky marshals be used and if our very serious concerns are met, we shall cooperate as best we can," McAuslan said.
Under the agreement, with an unnamed airline, the captain of a plane will be told who the air marshals are and where they sit. The pilot, who will remain in command during the duration of the flight, will also be in regular contact with the guards.
The pact also covers issues such as the weapons that can be used, insurance cover and the crew's legal liability, BALPA said.
The organisation, which represents the vast majority of Britain's 9200 airline pilots, said it hoped to roll out the pact across the airline industry.
Portugal opposes plan
Also on Wednesday, Portugal's pilots came out against the US proposal, arguing the measure would greatly jeopardize airline safety.
"Planes have many people inside a small space and it is easy for things to get out of control," the head of their SPAC union, Angelo Felgueiras, told private radio TSF.
"I have been on flights where there have been fist fights and I was grateful no one had a weapon," he added.
"Planes have many people inside a small space and it is easy for things to get out of control"
Head of SPAC union
Felgueiras said he believed the plan was well-intentioned, but he argued it would be better to tighten security on the ground.
He warned armed "sky marshals" could lose control of their guns to terrorists, or a bullet they fire could miss its target and damage key airplane equipment.
"The consequences could be dramatic," Felgueiras said.
The announcement by the United States on Monday that it was ordering foreign airlines to place armed marshals on selected flights drew a mixed reaction from international carriers and airline bodies.
The US Department of Homeland Security said the measure went into effect on Sunday under emergency amendments to federal aviation regulations.
The International Air Transport Association, which represents around 95% of airlines operating international flights, has opposed the decision outright.