Amnesty International activists wearing white mechanics' boiler suits delivered five replicas of the 1.8-metre-long Paveway-IV weapons used by British-supplied Saudi jets outside Prime Minister David Cameron's office.
"Ministers need to stop burying their heads in the sand and immediately suspend arms sales for the Saudi war machine," said Amnesty's UK director, Kate Allen.
The Saudi-led coalition began bombing Iran-backed rebels in Yemen in March 2015 to support President Abedrabbo Mansour Hadi, in a campaign that UN rights chief Zeid Ra'ad Al Hussein today said had killed 3,218 civilians.
It says it has raised allegations of civilian targeting with the kingdom, but refused a call by parliament's international development committee last month to suspend exports until the matter can be properly investigated.
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Under Britain's arms export criteria, licences cannot be granted if there is "a clear risk that the items might be used in the commission of a serious violation of international humanitarian law".
The government approved nearly USD 4.3 billion and USD 3.8 billion of arms licences for exports to Saudi Arabia in the six months to January, according to the international development committee.
"It is absolutely shocking that the UK is still selling billions of pounds' worth of weapons to Saudi Arabia even as the civilian casualties have mounted and mounted in Yemen," Allen added.
A second parliamentary committee, on arms export controls, last week launched an inquiry into the use of British manufactured arms in Yemen, and will hold its first evidence session next week.
The Campaign Against Arms Trade is also pursuing legal action against the government in a bid to suspend exports.