Two American flights carrying "hazardous cargoes" bound for Israel are due at Prestwick Airport to refuel this weekend.
The first of the two flights was expected on Saturday
It is unclear exactly what will be on board the planes.
However, campaigners fear they are carrying more hi-tech bombs to be used in the conflict in Lebanon.
US President George W Bush has apologised to Tony Blair over the previous use of Prestwick Airport to refuel planes carrying bombs to Israel.
The prime minister's spokesman said Mr Bush gave a "one-line" apology for the fact proper procedures had not been followed.
Some air traffic controllers at Prestwick, near Glasgow, have raised concerns about handling flights carrying bombs.
Residents and politicians in Ayrshire have also voiced anger at the airport's use as a stopover for the planes.
The Civil Aviation Authority has been conducting an inquiry into suggestions that previous landings may have broken the rules over notification of the cargo.
Foreign Secretary Margaret Beckett raised concerns with the US Government over the issue last week.
Her intervention came after newspaper reports that two chartered cargo planes filled with laser-guided bombs landed at Prestwick en-route to Israel from the US.
One flight carrying a "hazardous cargo" was expected to land at the Scottish airport on Saturday, with the other due to touch down on Sunday.
The planes are travelling from San Antonio in Texas to Tel Aviv.
A Civil Aviation Authority spokesman said: "They are hazardous material flights - the items that they are carrying are understood to be of a dangerous nature.
"They are landing at Prestwick for refuelling, and needed an exemption to be able to land in the UK. This was granted last week.
"Our concern in any of these cases is that the proper procedures have been carried out. We are purely looking at it from a safety point of view, and we are satisfied that our requirements have been met."
The planes will be refuelled at Prestwick
Liberal Democrat leader Sir Menzies Campbell said the flights were "adding insult to injury".
"What price the president's apology now?" he asked.
"Who can tell if some of this equipment may be used to continue Israel's disproportionate attacks on Lebanon?
"The British government should be pursuing an active policy of denying weapons of any kind to anyone in the Middle East who may be assisting the conflict in any way."
The Scottish National Party's deputy Westminster leader, Angus Robertson, said there was an issue of principle at stake.
"President Bush's supposed one-line apology for breaching procedures at Prestwick is not good enough," he said.
"Scotland should have no part in conflict escalation while hundreds of children are dying in Lebanon and across the Middle East."