US plans to base part of a missile defence system in Poland must be matched with a commitment to deploy weapons to protect Polish air space, the new Warsaw government said on Monday in an early indication that it intends to stand by election promises to adopt a more assertive stance towards Washington.

Bogdan Klich, defence minister, said Warsaw would have to undertake a “new ­attempt at balancing the benefits and costs” of allowing the US to build a base on Polish territory to hold 10 anti-missile interceptors.