SOFIA, Nov. 7 (Xinhua) -- The European Union (EU) needs to build a common defense but many challenges remain, said Constantin Popov, chairman of the defense committee of the Bulgarian parliament on Thursday.

"Security is our common task, our common goal, and we Europeans have to seek a common answer," Popov said in a keynote speech at the opening ceremony of an international conference on European defense.

Popov said it is natural for the EU to build common capabilities in order to give European citizens more security.

A lot of work has been done in recent years to enhance the EU's defense capacity, "but there are still many unresolved issues that need to be addressed," said Popov, Bulgaria's former chief of defense.

Popov said the development of EU security was related to the development and future of the EU, adding that "all countries have to participate in the development of the common system, and to receive the common and full EU guarantees for their security."

Popov said he saw no particular reason to build a common European army at this stage. "This means that our national armies will continue to be the backbone of the European defense."

The senior official noted that European defense could not be built as an alternative to NATO.

"NATO will remain a cornerstone of European security and defense."

The bloc has to tackle many key issues, such as Brexit, transatlantic cooperation, and post-Brexit cooperation between the EU and Britian, Popov said.

"As you can see, we have more questions than answers," Popov said.