Leaders of the North Atlantic Treaty Organization have kicked off a 2-day summit in Spain. NATO officially invited Sweden and Finland to join.

The Nordic countries applied following Russia's invasion of Ukraine -- a key topic at the meeting.

NATO Secretary General Jens Stoltenberg said all 30 members have ratified the decision to issue a formal invitation to Finland and Sweden to join the alliance.

The invitation came after Turkey agreed to lift its veto of the two nations joining the alliance, which requires unanimous support of current members.

Moscow reacted swiftly. A senior foreign ministry official told reporters the expansion of NATO is a destabilizing factor.

Leaders at Wednesday's summit agreed to step up support for Ukraine. They also endorsed a new strategic concept, which describes Russia as a direct threat.

NATO is turning its attention toward China as well. It says Beijing poses challenges to its security, interests and values.

Leaders of non-NATO states are taking part in the discussions, including Japan's Kishida Fumio and South Korea's Yoon Suk-yeol.