Egyptian authorities say there has been a serious incident near the airport used by the multinational observer force in the Sinai Peninsula.
Initial reports indicating that a bus had exploded, causing casualties, have been denied by officials.
A blast reportedly occurred outside an airport at al-Gorah, the force's main camp in the north of Sinai.
The Multinational Force and Observers (MFO) monitors Israeli and Egyptian adherence to the Camp David Accords.
A vehicle carrying force personnel appeared to be hit by a blast about 1km outside the base which is near the town of el-Arish.
Egyptian officials said that the explosion was likely to have been caused by an unexploded landmine left over from conflicts with Israel, but this could not be confirmed.
Sinai was the scene of three Arab-Israel wars between 1956 and 1973.
Under 1978 peace accords between Israel and Egypt, both sides undertook to maintain the Sinai as a demilitarized zone.
The MFO operation is not run by the United Nations.