The announcement comes after the two countries in October signed another letter of intent on aviation cooperation, which Swedish Prime Minister Ulf Kristersson said could lead to Ukraine buying up to 150 of Sweden's Gripen E fighter jets.

"This will strengthen our shared ability to develop and produce new battlefield technologies," Swedish Defence Minister Pal Jonson said at a press conference.

The plans would see Swedish personnel working on site in Ukraine, he said.

Ukraine will share its battlefield expertise, and Sweden will draw on its experience in developing advanced weapons systems, the minister added.

Speaking alongside Jonson, his Ukrainian counterpart Denys Shmygal added the two countries already had "many agreements and concrete letters of intent, or even contracts between Swedish and Ukrainian companies."

He declined to name any companies, concerned that "Russians will destroy their facilities".

The two countries aim to start the cooperation as soon as possible, Shmygal added.

Jonson also said the countries had continued talks on deliveries of the Gripen E jets to Ukraine and "agreed on establishing a joint working group to move this forward".

Shmygal explained that four financing options were being considered, including the use of frozen Russian assets, Swedish contributions to Ukraine, fundraising from European partners, and funding through international organisations.

The Ukrainian minister stated that he was ready to send pilots and mechanics to Sweden immediately to train on the Gripen systems.

While he said Ukraine was ready to sign a contract on ordering the modern model E in the future, they would "ask Sweden as a friend" to transfer existing fighter jets -- meaning older models -- "to protect our sky directly next year".

Last year, Sweden suspended plans to send its Gripen fighter jets to Ukraine, after partner countries requested that priority be given to American F-16s.