LONDON — US President Barack Obama warned British Prime Minister David Cameron against allowing defense spending to slip below NATO's target of 2 percent of gross domestic product when the two leaders met in Washington last month.

Obama warned that failure to meet the NATO spending target would undermine the NATO alliance and that if Britain didn't step up and meet the budget goal then nobody else in Europe would either, the Daily Telegraph reported Wednesday.

The US pPresident is the latest, and most important, of a string of top US gGovernment officials to warn Britain of the implications of falling defense spending.

Ex-US Defense Secretary Robert Gates and others have made similar points over the last few years as Britain slashed defense spending as part of government financial austerity measures. implemented by the gGovernment.

British defense spending at just over £33 billion (US $50.3 billion) already hovers close to the 2 percent target but with further big cuts to government budgets expected on the other side of the May general election, who ever wins ,the forecast is that the NATO guideline will be breached whichever party wins.

A cross-government spending review is scheduled to follow the election as Britain continues to wrestle with ailing public finances. Only health, education and overseas aid budgets have so far been exempted from further cuts.

Leaking of the conversation between Obama and Cameron further cranks up growing pressure from politicians and others to raise the issue of defense cuts ahead of the election.

Last week, two former defense ministers from the Conservative and Labour parties added their names to a parliamentary motion demanding the government continue to meet its 2 percent spending pledge.

To date, the Conservative-led coalition government has failed to guarantee Britain will maintain spending at or above the 2 percent beyond the next financial year starting in April despite having pushed for European NATO members to meet the mandated 2 percent level at the alliance held summit in Newport, South Wales, last September.

A report released by the Royal United Services Institute think tank to coincide with the summit said depending on the size of any defense cuts and other factors, like economic growth, by 2020 British spending on the military could account for as little as 1.6 percent of GDP.

Only Britain, the US, Greece and Estonia currently meet the NATO spending requirements, and with the threat from Russia and the deteriorating security situation in the Middle East, there has been increasing pressure being applied for European nations to reverse the trends of recent years and hike defense spending.

In its annual Military Balance report released Wednesday,today the International Institute for Strategic Studies (IISS) in London said that European defense spending continued to fall last year although akthoiugh the decline slowed compared with previous years.

Spending was down 1.75 percent overall last year, slightly less than the 2 percent per annum average decline since 2010, said IISS.

Howard Wheeldon, of consultants Wheeldon Strategic, said Obama's concern over the impact that Britain reneging on its commitments might have on other NATO members is genuine.

"Not only will the UK fall well behind the NATO alliance target of 2 percent GDP spend on defense, but that if it does, the commitment made at the NATO summit in Wales that all member states should work toward the 2 percent target spend is worthless," he said.

"By taking another £1.5 billion out of defense, a figure being banded around in Treasury and Ministry of Defence circles, and assuming that the UK GDP continues to improve as a result of continued growth, I could see UK defense spending coming down as low as 1.6 percent of GDP by 2020," Wheeldon said.

A spokesperson for the British prime minister defended Britain's defense spending record but failed to give any commitment to maintaining the 2 percent level after 2016.

"With the second largest defense budget in NATO and the largest in Europe, the government is committed to spending 2 percent of GDP on defense. Decisions on spending after the financial year 2015/16 will be determined in the next spending review.

"During the prime minister's recent visit to Washington, the president made the point that the US greatly appreciates that the UK currently meets the 2 percent target," said the spokesperson.