The company said models WMAQC641PUK, WMAQG741PUK and WMFG741GUK will be added to the recall list, and that it would contact all owners of the machines it is aware of.
The model numbers can be found in the recess inside the door or on the back of the appliance.
It said in a statement: "Nearly two million people have contacted Whirlpool to check if their washing machines are part of the recall since the company announced the safety issue in mid-December.
"Over 90% of these people have been given peace of mind that their appliances are not affected."
The recall started when customers discovered flaws with the washing machines' door locking system that can cause the devices to overheat and catch fire.
The problem affected Hotpoint and Indesit branded products sold in the UK between October 2014 and February 2018.
Whirlpool vice president Jeff Noel said: "We are hugely grateful to everyone who has already come forward and we urge all remaining owners to please get in touch with us as soon as possible.
"While this is good progress, we know there is still work to do. That's why we are working seven days a week to look after our customers and running a widespread campaign to raise awareness.
The company has offered to replace or repair all the affected washing machines, but consumer group Which? said it has been contacted by many customers who fear waiting for a fix.
Sue Davies, head of consumer protection at Which?, said: "It would clearly be unacceptable if customers were left for many months without adequate washing facilities in their homes, particularly when there is also no offer to cover consequential costs such as trips to the laundrette.
"The company should do the right thing and offer customers a refund, so people can get fire-risk machines out of their homes and quickly find a suitable replacement."