U.S. Secretary of State Rex Tillerson, in his first talks with NATO counterparts in Brussels, discussed funding the alliance.

BRUSSELS U.S. Secretary of State Rex Tillerson warned NATO allies Friday to boost defense spending or come up with plans to reach the alliance's budget guidelines within two months.

Tillerson, in his first talks with NATO counterparts in Brussels, said that Washington is spending a "disproportionate share" on defense compared with its 27 partners, and that he expects action by the time President Donald Trump meets with other alliance leaders on May 25.

NATO leaders pledged in 2014 to halt defense spending cuts and move toward a guideline target of 2 percent of gross domestic product within a decade. Only four other nations currently meet the target: Britain, Estonia, Greece and Poland.

"Our goal should be to agree at the May leaders meeting that by the end of the year all allies will have either met the pledge guidelines or will have developed plans that clearly articulate how, with annual milestone progress commitments, the pledge will be fulfilled," Tillerson told the ministers.

Tillerson did not say what would happen if European allies and Canada fail to respect their pledges. During election campaigning, Trump suggested that he might not come to the defense of those allies who do not do their fair share, rocking allies near an increasingly aggressive Russia, such as Estonia, Latvia, Lithuania and Poland.

However, Tillerson sought to calm any fears, saying Friday that "we understand that a threat against one of us is a threat against all of us, and we will respond accordingly. We will uphold the agreements we have made to defend our allies.

The United States is by far NATO's most powerful ally. It spends more on defense than all the others combined; 3.61 percent of GDP in 2016, according to NATO estimates, although U.S. spending, too, has tapered off in recent years.

Germany spent 1.19 percent of its overall budget on defense last year.

But German Foreign Minister Sigmar Gabriel said it would be "unrealistic" for his country to hike spending from 35 billion euros ($37 billion) a year to over 70 billion euros, which would see Berlin allocate more to defense than Russia currently.

"I don't know a politician in Germany who believes that this would be achievable or even desirable," Gabriel said.

He said security is also about crisis prevention, not just combat, and noted that Germany spends a lot of money on refugees who arrive because military interventions have failed.

Seven countries including Canada, Italy and Spain would have to virtually double their spending to reach the target.

Canadian Foreign Minister Chrystia Freeland said that beyond money, "it's also really important to look at capabilities and what countries are actually doing."

"We really feel that we're doing our share," she said, highlighting Canada's troop deployment to Latvia to help deter Russian aggression.