Poland has strengthened its air defence measures after a series of alleged violations of its airspace in recent weeks. On September 17, the Polish Air Force began precautionary patrols intended to protect the eastern section of the country’s airspace. Related developments • item 1 of 4Ukraine says two North Korean prisoners of war were transferred to South Korea • item 2 of 4Russian strikes kill eight across Ukraine as Washington increases diplomatic efforts • item 3 of 4Russia targets Ukraine