(Adds Gabriel comments in paras 2, 5-7)
By Sabine Siebold
TALLINN, March 1 (Reuters) - NATO has not agreed on every nation in the alliance having to meet a spending target of 2 percent of its gross domestic product on defence, German Foreign Minister Sigmar Gabriel said on Wednesday on a visit to Estonia.
European governments have come under pressure to increase their defence budgets since the election of U.S. President Donald Trump, who has been critical of spending commitments by Washington's NATO allies.
"I have a concern that politicians make public promises that they can't fulfill later on," said Gabriel.
He said that NATO had merely agreed that member nations would make efforts to reach the 2 percent target.
"There is no apodictic 2 percent goal but rather ... we should be moving in that direction," he said. Germany now spends 1.2 percent of GDP on defence.
Defence spending has become a source of tension in the loveless coalition of Chancellor Angela Merkel's conservatives and Gabriel's centre-left Social Democrats. The Social Democrats hope to unseat their senior coalition partner in September's federal election.
At a NATO summit in Wales in 2014, allies agreed to end years of defense cuts that left Europeans without vital military capabilities. They agreed all allies should reach the target of spending 2 percent of economic output on defense every year by 2024, although the goal is not legally binding.
In Tallinn, Gabriel said Germany would not refuse to increase defence spending.
But he added it was "completely unrealistic to raise expectations in Germany or among our partners that we will add 30 billion euros to our defence spending over the next eight years" -- the amount required to take German defence spending to 2 percent of GDP.
Defence Minister Ursula von der Leyen, a conservative, has criticised Gabriel for separate remarks he made at the Munich Security Conference, where he warned against focusing solely on defence spending and unleashing a new arms race.
Von der Leyen recently said Germany was boosting military spending by nearly 2 billion euros in 2017 to 37 billion euros, or 1.22 percent of GDP. It is due to reach 39.2 billion euros by 2020.
Merkel has said Germany needed to fulfill its commitment to boost defence spending to meet NATO's target of 2 percent.
In contrast, Gabriel has in recent weeks raised doubts about whether Germany, a country wary of heavy military spending since World War Two, should pour more money to defence.
The foreign minister has said Germany must keep in mind its military past. His stance strikes a chord among left-leaning voters.
(Reporting by Sabine Siebold; writing by Erik Kirschbaum; editing by Michael Nienaber and Richard Lough)