Two British transport planes were deployed to the Sinjar region, where extremist Islamic State militants are on the offensive, on Saturday, a ministry spokesman told AFP.
The United States carried out air strikes and aid drops as President Barack Obama vowed to help thousands of civilians besieged by jihadists on an Iraqi mountain starting on Friday.
President Obama gave no timetable for the first US operation in Iraq since the last American troops withdrew three years ago and put the onus on Iraqi politicians to form an inclusive government and turn the tide on jihadist expansion.
US forces hit out on the campaign's second day to protect members of the Yazidi minority, many of whom have been stranded on Mount Sinjar since they fled IS attacks on their homes a week ago.
US forces "successfully (conducted) four airstrikes to defend Yazidi civilians being indiscriminately attacked" near Sinjar, the United States Central Command, which covers the Middle East, said in a statement on Saturday.
In the first strike, "a mix of US fighters and remotely piloted aircraft struck one of two ISIL armoured personnel carriers firing on Yazidi civilians near Sinjar", the statement said.
After following the remaining vehicle, a second pair of strikes, around twenty minutes later, hit two more armoured personnel carriers and an armed truck.
The fourth, struck another armoured personnel carrier also in the Sinjar area.
US and Iraqi aircraft have also sent planes to deliver food and water to the thousands of people, many of them Yazidi civilians, stranded on the mountain.
The third US airdrop, announced by Centcom late Saturday, sent thousands of litres of water and more than 16,000 packaged meals to the besieged civilians.
"The United States can't just look away. That's not who we are. We're Americans. We act. We lead. And that's what we're going to do on that mountain," Obama told reporters Saturday.
President Obama had previously said the US was intervening to "prevent an act of genocide".
France and Britain announced that aid consignments of their own were imminent.
Two Royal Air Force (RAF) C-130 transport planes took off from Britain Saturday carrying reusable filtration containers filled with clean water, tents, tarpaulins and solar lights that can also recharge mobile phones.
The Yazidis, who worship a figure many Muslims associate with the devil, are a small and closed community, one of Iraq's most vulnerable minorities.
Security sources and a local official said the bodies of 16 Sunni extremists killed in Makhmur, where IS positions were bombed on Friday and fighting with peshmerga also took place, had been buried nearby on Saturday.
Federal and Kurdish officials, who had been at loggerheads since IS fighters launched their an offensive exactly two months ago that has brought Iraq to the brink of partition, have said they were now working together and with US advisers.
Up to 100,000 Christians were forced to flee from their homes in a matter of hours on Thursday, completely emptying the country's largest Christian city Qaraqosh of its population.
Among the hundreds of thousands of people who fled their homes in northern Iraq were several other minorities such as the Shabak and Turkmen Shiites.
UNESCO chief Irina Bokova called it an "emerging cultural cleansing".
Obama said he was confident the US could prevent IS fighters "from going up the mountain and slaughtering the people who are there" but added the next step of creating a safe passage was "logistically complicated".
