BRUSSELS (AP) — Dutch King Willem-Alexander used a speech to the European Parliament on Wednesday to make a plea for unity less than a month before Britain's referendum on whether to remain in the 28-nation bloc.

Willem-Alexander told lawmakers in Brussels that the "European bouquet" is not complete "without the English rose."

The king also highlighted shortcomings that have strained relations in Europe and fed growing skepticism toward the bloc among its 500 million citizens. British citizens will vote on whether or not the country should stay in the EU on June 23.

Willem-Alexander said that by concentrating on "essential issues which truly require a common approach," the EU will become more effective and can address concerns that its powers are too sweeping and centralized.

The Netherlands is a founding member and strong supporter of the EU, but it also rejected the bloc's proposed constitution in a 2005 referendum.

The monarch's message was generally pro-Europe.

"Great things are rarely achieved at purely national level," he said, adding that EU members need to join forces to tackle pressing problems such as the refugee crisis, violent extremism, and climate change.

"In all these challenges, we need each other," he said.

The speech prompted a sharp response from populist anti-Islam and Euro-skeptic lawmaker Geert Wilders, whose Freedom Party is riding high in Dutch polls. Wilders asked Prime Minister Mark Rutte in a written question to Parliament: "Is it correct to conclude from these words that the King is opposed to a possible exit of the United Kingdom from the EU?"