Military action in Syria must be matched with urgent additional funding to support veterans suffering with mental health problems, a charity has said.
Combat Stress is already struggling to cope with an unprecedented increase in demand from ex-servicemen and women needing treatment for post-traumatic stress disorder (PTSD), anxiety and depression.
In the last financial year referrals to the charity went up by nearly 25% from 1,819 in 2013/14 to 2,328 in 2014/15.
The charity is taking a seven-figure sum from its reserves to keep its services running, including three rehabilitation centres.
A spokesman warned that if no additional funding is found the charity's services will look drastically different within four years.
As RAF air strikes are launched in Syria and referrals to the charity are expected to continue to increase, Combat Stress has warned that it might not be able to afford to support veterans in the future.
It is currently treating nearly 6,000 ex-servicemen and women, of which more than a third (2,156) served in Afghanistan or Iraq. It is the highest number of patients on the charity's books since its launch in 1918.
Combat Stress said 20% of servicemen and women suffer with mental health problems and 4% are diagnosed with PTSD.
Robert Marsh, fundraising and communications director, said: "Following a decade of military action in Iraq and Afghanistan, we are now struggling to cope with the thousands of veterans seeking our specialist mental health services.
"It is vital we have the resources available to make sure everyone who needs specialist support has timely access.
"With MPs supporting further military action, we urgently need the financial resources to ensure our unique service continues to help the thousands of brave veterans who deserve the very best treatment."