"We are open to see the project becoming a project of regional cooperation," the Polish minister told BNS.

Asked again whether Warsaw was inviting Vilnius to develop missile defense capacities together, Siemoniak stated that searching for partners would be part of the next phase, which is yet to be started.

"We want the programs to be open and targeted at our partners in the European Union (EU) and NATO. However, I think it is too early to discuss the details. Without doubt, I want to emphasize that after today's highly successful conversations, Lithuania is our very important partner in military cooperation," the minister said in an interview on Thursday.

"However, these are things of such a caliber that they require highly specific and in-depth negotiations before being announced to the public. On the other hand, we in Poland have to know precisely what we can propose to whom, and we haven't reached the phase yet," Siemoniak said.

"On Friday, our president will sign a law that guarantees funding for air defense, including missile defense, for the coming years. On the other hand, we are currently working to establish the concepts and possibilities we may find interesting. Searching for partners will be in the next phase," he added.

The Polish defense minister emphasized that the missile defense system being developed in Poland is "an element of the common system also built by the United States."

In his words, the Polish project has nothing to do with the US decision to give up one of the NATO missile defense system elements in Europe, as the Warsaw plans were announced much earlier.

"What is being built by NATO and the United States is missile defense against medium-range missiles; however, we want to develop our system in a way to defend ourselves against short-range missiles," Siemoniak noted.

In March, the US announced plans to give up the fourth phase of the missile defense, which was supposed to involve modernization of the three completed phases and intended to take over missiles aimed at the US and flying across Europe.

Officials say the most important part for Europe and Lithuania is to have the US keep its promise of implementing phases two and three, which include radars and missile traps in Romania and Poland. Aimed at providing defense against Iranian missiles, the phases should be completed by 2018. Once implemented, the missile shield will cover all of NATO's European territory.

Poland first mentioned its new regional security initiatives last year.

At a meeting with Poland's Prime Minister Donald Tusk, Lithuania's then PM Andrius Kubilius said he was briefed on "initiatives covering matters related to the development and strengthening of a wider Central and Northern European region." Kubilius described them as “new and interesting ideas” but refused to elaborate any further.