U.S. Army Chief of Staff Gen. Raymond Odierno said on Sunday that he was “very concerned” about recent cuts by Britain to its defense budget. Odierno said the cuts forced a review of how U.S. troops would work alongside their British counterparts, with the latter's units possibly operating within U.S. ranks, instead of alongside each other.

Britain has cut its defense budget by around 8 percent since the new coalition government came to power in 2010, affecting the army, the Royal Air Force (RAF) and the Royal Navy, Reuters reported. As a result of the cuts, the British army has lost a fifth of its troops, the air force has only seven combat squadrons, and the navy is barely capable of maintaining its ongoing international duties, according to The Telegraph. Troops from both countries are working together in several conflict zones around the world, including in Iraq, Syria and Afghanistan.

Odierno said Britain needed to maintain its commitment to NATO targets in the face of global instability, adding: “This is the most uncertain global environment I have seen in 40 years of service,” The Telegraph reported.

Few countries have met NATO's target for its member nations to spend a minimum of 2 percent of GDP on defense. The commitment was relaxed in September to say that countries should “halt any decline in defence spending,” according to the European Leadership Network (ELN).

However, the U.K., Germany, Italy, Canada, Hungary and Bulgaria are set to cut their defense budgets. And while Poland, Latvia, Lithuania, the Netherlands, Norway and Romania will see spending rise, only Estonia will meet NATO's target in 2015, ELN reported.

U.K. Prime Minister David Cameron has come under fire for failing to promise an end to budget cuts, with members of his Conservative party accusing him of failing to make defense a priority at a critical time.

“It would be damaging to the United Kingdom if we were to fail to do so,” Gerald Howarth, a Conservative Member of Parliament and former minister of defense, said in an interview with Radio 4, The Press Association reported. “It would diminish us in the eyes of our closest allies. Conservatives believe defense of the realm is the first duty of government.”