The Ministry of Defence told ITV Wales that it's "not impossible" that a military aircraft was flying low over the Pembrokeshire coast last night.
It follows concerns that an aircraft had gone into the sea at Trefin near Fishguard - a search and rescue operation was was later stood down.
Witnesses had reported a loud blast in the area shortly after 7pm, but an MOD spokesman said it was "highly unlikely" this was a sonic boom.
"Breaking the sound barrier over land is prohibited by regulation," said the spokesman.
"The only time a pilot would do it is in an emergency situation."
Milford Haven Coastguard have told ITV News that they believe two military aircraft flying in the area have returned safely to base, after initial reports of a plane crash.
People in Trefin reported two planes flying low overhead yesterday evening and a loud blast moments later.
The air and search operation launched after a suspected plane crash near Fishguard has been "stood down."
Milford Haven coastguard told ITV News they "don't believe there's anything in the area."
The Ministry of Defence has confirmed that no military aircraft has been involved in a crash.
ITV News understands the jet that is believed to have crashed off the Welsh coast is likely to be UK-based.
Dyfed Powys Police have said they are aware of reports of a possible plane crash off the coast of Pembrokeshire and are investigating the claims.
A major air and sea search operation is underway near Fishguard, Pembrokeshire, amid reports that a plane may have crashed.
Residents in Trefin reported two fast jets flying low overhead just after 7pm. There were also reports of a loud blast moments later.
A rescue helicopter from RAF Chivenor in addition to two all-weather RNLI lifeboats have been called by Milford Haven coastguards.