Almost all member states of the EU Eastern Partnership initiative have advanced in their development, U.S. Secretary of State John Kerry said in his address to the Eastern Partnership summit opening in Vilnius.

The address was read out at a civil society conference in Vilnius on Thursday.

Kerry said at the same time that serious challenges remained in the fields of the freedom of speech, the media and corruption.

He stressed the importance of contributions from civil society, which he described as a locomotive force in the development of the law-governed state.

Average citizens of each member country - Armenia, Azerbaijan, Belarus, Ukraine and Georgia - play a prominent role in the continuing integration with the international community and this is very important, Kerry said.

A two-day summit of the Eastern Partnership initiative opens in Vilnius on Thursday.