"A bomb exploded near the outer wall of UNRWA's headquarters in Gaza, some 10 metres (yards) from the gate, without causing any injuries or damage," agency spokesman Adnan Abu Hasna told AFP.
The Hamas-run security forces also confirmed the blast, saying they had opened an inquiry after "two homemade bombs" exploded, one outside UNRWA and a second elsewhere in the city, causing slight damage but no injuries.
The incidents took place just hours before members of the Ramallah-based Palestinian cabinet were to visit Gaza.
They have also targeted both public buildings and private homes and cars.
In December, an explosive device went off by the French Cultural Centre in Gaza City, the most visible foreign presence in the tiny enclave, which is home to 1.8 million people.
Such incidents, which have increased since last summer's deadly conflict with Israel which left some 2,200 Palestinians dead, are never claimed.
