By Andrea Shalal

WASHINGTON (Reuters) - Republican presidential nominee Donald Trump threatens U.S. and world security with his "politics of fear and isolation," German Foreign Minister Frank-Walter Steinmeier said on Wednesday.

Steinmeier, a Social Democrat, told Reuters in a written interview that he was concerned about what he called Trump's ambiguous vows to "make America strong again" while simultaneously reducing its engagement overseas.

"A politics of fear and isolation will bring less security, not more, and would be dangerous not only for the United States, but for Europe and the rest of the world as well," he said before departing for Washington for meetings about the U.S.-led effort to defeat the Islamic State militant group.

Trump secured his party's 2016 presidential nomination on Tuesday, having overwhelmed his rivals in the state nominating contests and rolled over skeptical members of the Republican establishment.

Upon his arrival in Washington, Steinmeier told reporters that Europeans were anxiously awaiting Trump's acceptance speech at the Republican National Convention in Cleveland on Wednesday for clues as to what his policies would be toward Europe.

"We Europeans expect a speech from the Republican candidate which contains more than just promises to make America stronger. We are interested in what that means with a view of the world and the relationship with Europe," Steinmeier said.

Steinmeier has blasted Trump for months for his "America First" speech, while praising Democrat Hillary Clinton as an experienced foreign policy expert.

The German politician said the current crisis-charged world situation tempted people to look for easy answers. However, the challenge is to find solutions that work and do not rely on simple slogans or the erection of new barriers, he said.

Steinmeier was among the vocal critics of Trump's first major foreign policy address in April, in which the real estate tycoon repeatedly promoted an "America First" agenda, rejected last year's nuclear deal with Iran, called for more investment in missile defense in Europe, and accused the Obama administration of tepid support for Israel.

Trump's comments during the campaign - including calls to ban Muslims from the United States - have raised alarm among U.S. allies unnerved by the phrase "America First," which was used in the 1930s by isolationists who sought to keep the United States out of World War Two.

(Reporting by Andrea Shalal; Editing by G Crosse and Paul Simao)