On the morning of 17 February, the Greek border garrison came under heavy fire from Albania. This incident was one of the biggest in a series of border conflicts between the two states in the second half of the 1940s.

In most cases, the Greeks were on the defensive, and Albanian attacks were limited to illegal forays into Greek territory, cattle raiding, and kidnapping. However, on 17 February the aggression reached a new level – the situation escalated into an armed conflict between regular military formations.
Albania had effectively been at war with Greece since 28 October 1940 when it joined the Axis powers as a satellite of Italy. However, Albania's new communist government rejected claims of their country's collaboration with the Nazis, since it was formed from members or supporters of the Resistance. (The partisans’ Albanian National Liberation Army forced the Italians to capitulate and expelled the invaders unaided).
Greece was expected to suffer the same fate as Albania, but the attempted Italian occupation of Greece proved unsuccessful, and the German forces took over. As a result, Greece became one of the principal victims of World War II in terms of human and economic damage.
Long-standing territorial disputes between the two countries escalated following the war. Unable to resolve the territorial problem, the Albanian government repressed Albania's ethnic Greeks, sending most of them to concentration camps. For its part, Greece appealed to the world and prevented Albania from joining the United Nations. Yugoslavia repeatedly initiated Albania's inclusion in the UN, but Greece, enjoying UK support, managed to prevail in this diplomatic dispute.
Albania would become a member of the UN only on 14 December 1955.
Source:
United Nations Digital Library https://digitallibrary.un.org/