The BBC has learned of a foiled al-Qaeda plot to blow up the British embassy in Yemen, weeks before the bombings in Istanbul.
The embassy in Yemen has been reinforced by concrete blocks
Twenty militants confessed to planning to crash a truck bomb through the embassy gates in Sanaa, BBC Security correspondent Frank Gardner reports.
Security officials say they were receiving instructions from al-Qaeda operatives in Iran.
The British Consulate in Istanbul was destroyed in a bomb attack last month.
The BBC's Frank Gardner visited the Yemeni capital Sanaa for the Ten O'Clock News.
He visited a government checkpoint outside the city, which is part of a drive to eradicate al-Qaeda.
Checkpoint commander Colonel Abdullah said his men were trying to match faces with photographs of al-Qaeda suspects.
"We are searching the cars for anyone carrying guns, and also for anybody who resembles a known terrorist suspect," he said.
Our correspondent says the planned attack on the British embassy, which lies on a busy street, would have been devastating if the plotters had not been captured three months ago.
The alleged plotters drove around the embassy, videoing every angle, looking for weak points.
The video has been sent to London for analysis.
"We are very conscious that we are a high priority target here in Yemen," the British ambassador Frances Guy told the BBC.
"We try our best on a daily basis to review our security and improve it as much as we can."
Concrete blocks have been placed outside the embassy to stop truck bombs. The ambassador travels with a close protection team of armed bodyguards.
Our correspondent says thanks to improved Yemeni intelligence the bomb plot was thwarted before the would-be bombers got hold of explosives. But he says the embassy remains a target.
Twelve people died in the November bombing of the British consulate in Istanbul, Turkey, including the consul general Roger Short. The headquarters of the HSBC bank was also targeted, and the total fatalities in both attacks reached more than 60.
Our correspondent says the arrests in Yemen has raised the question of whether the Istanbul attack could have been prevented.
The UK Foreign and Commonwealth Office declined to discuss what extra precautions had been taken at embassies in the region since the discovery of the plot.
Instead they issued a statement:
"We never comment on the security of individual buildings for good reason. But the security of our staff is paramount.
"There is no one-size-fits-all approach to security."