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Secretary of State Rex Tillerson arrives in Brussels for his first NATO meeting on Friday pushing the U.S. agenda of increased defense spending by member states and a greater role in the fight against terrorism before President Trump arrives in May.

NATO member countries have until 2024 to meet a shared pledge to spend 2 percent of their gross domestic product on defense but the Trump administration is unapologetic about wanting to see allies “do more, faster.”

"It is no longer sustainable for the United States to maintain a disproportionate share of NATO's deterrence and defense spending," a senior State Department official told reporters on Tuesday.

Outside of the U.S. which spends over 3.5 percent of its GDP on defense spending, four NATO members including Greece, Estonia, the U.K. and Poland cross the 2 percent mark. Others such as France and Turkey are nearing the target.

NATO alliance member Germany ,who President Donald Trump has said owes “vast sums of money,” spends 1.2 percent.

German Defense Minister Ursula von der Leyen rejected Trump's claim, saying that "there is no debt account at NATO."

Overall defense spending among European allies has increased over the last year but Secretary Tillerson will push for a clearer demonstration of allies’ commitment.

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“Everybody that’s not there yet, they have to have a credible plan that they can demonstrate to other allies to reach 2 percent,” the State Department official said.

The State Department has not specified consequences should member states fail to meet the goal.

“It’s not like this is a favor to the United States. The purpose of this, of this commitment, is to improve the security for all of us in the transatlantic region,” the official said.

President Trump has recently voiced strong support for the 70 year alliance he once called “obsolete,” but past suggestions that the U.S. might not protect allies unless they boosted defense spending has created uncertainty amongst European allies.

Mixed signals over Tillerson’s intention to attend the NATO’s meeting has done little to allay concerns.

A State Department spokesperson initially indicated the secretary would skip the NATO forum, later clarifying the agency was working with NATO on alternate dates. The gathering of top NATO diplomats was originally scheduled for April 5 and 6 overlapping with Chinese President Xi Jinping’s visit to the United States and a summit with President Trump.

The 27 other NATO members later agreed to reschedule the meeting to March 31 to allow the U.S. Secretary’s participation.

Tuesday, foreign ministers from Baltic States Estonia, Latvia, and Lithuania expressed confidence in U.S. support for the institution shortly before meeting with Tillerson in Washington.

Montenegro will also be represented at the NATO meeting. The U.S. Senate voted Tuesday in favor of expanding the alliance to allow that nation to join. The legislation is now awaiting the President’s signature.

Concern over Tillerson’s attendance to the NATO meeting was magnified by State Department officials confirming the Secretary would travel to Moscow later in April.

Russian and NATO officials will be meeting in Brussels in the NATO-Russia Council Thursday, less than 24 hours before Tillerson arrives.

The NATO-Russia Council (NRC) was suspended in 2014 following Russia’s role in the Ukraine crisis and the annexation of Crimea. This will be the fourth meeting of the NATO-Russia Council (NRC) since the forum resumed almost a year ago. The last meeting took place in December.

A NATO official told NBC News on Tuesday there was no relation between the scheduling of the two meetings. A senior State Department official said the meeting was agreed to before the Friday ministerial meeting was set.

“NATO is open to meaningful and constructive dialogue with Russia. Our practical cooperation with Russia remains suspended, but channels of political dialogue remain open, and the upcoming meeting of the NATO-Russia Council demonstrates that,” the NATO official said.

The senior State Department official told reporters Tuesday the agenda for the council meeting is "pretty standard" and would be focused on Ukraine, both pushing the Russians end their occupation of Crimea and honor their commitments under the Minsk agreement.

"We're trying to find ways to mitigate the chances of military incidents and risks," the official said.