Jihadists linked to the Islamic State have attacked a UN base and overrun a humanitarian hub in northeastern Nigeria, trapping 25 aid workers, security and humanitarian sources said. Scores of Islamic State West Africa Province (ISWAP) fighters invaded the town of Dikwa in restive Borno state, dislodging troops from the military base and torching the humanitarian hub, a military source told AFP on Monday. A spokesman for UN chief Antonio Guterres confirmed only that there was a “security incident”, but gave no further details.