Illinois Republican Rep. Aaron Schock abruptly announced his resignation on Tuesday, after facing questions for weeks concerning his lavish spending from government and campaign accounts. 

In a statement that took congressional leaders by surprise, the congressman said he would resign, effective March 31, "with a heavy heart." 

"Serving the people of the 18th District is the highest and greatest honor I have had in my life. I thank them for their faith in electing me and letting me represent their interests in Washington. ... But the constant questions over the last six weeks have proven a great distraction that has made it too difficult for me to serve the people of the 18th District with the high standards that they deserve and which I have set for myself," he said. 

Schock has faced mounting accusations of using taxpayer dollars for personal expenses and claiming questionable reimbursements. 

He started facing scrutiny after it came to light that he had decorated his office in the theme of the PBS program "Downton Abbey." A public watchdog group later filed a federal ethics complaint against him for using congressional money to redesign that office -- and for billing taxpayers or his campaigns tens of thousands of dollars in private air travel on donor-owned planes.

On Monday, the Associated Press confirmed that the Office of Congressional Ethics had reached out to Schock's associates as it apparently began an investigation. The office is an outside panel that reviews ethics complaints against House members and makes recommendations to the House Ethics Committee. 

Fox News is told by multiple sources that Schock did not notify Republican congressional leaders before making his announcement on Tuesday. 

Speaker John Boehner said in a statement: "With this decision, Rep. Schock has put the best interests of his constituents and the House first. I appreciate Aaron's years of service, and I wish him well in the future." 

Democratic Sen. Dick Durbin, also of Illinois, called the resignation a "surprise" and said it "reflects the gravity of his situation." 

Details emerged Monday of another business deal between Schock and one of his political donors. 

The Associated Press reported a shell company linked to Schock paid a political donor $750,000 last year for a warehouse in Peoria, then took out a $600,000 mortgage for the property from a local bank run by other donors, a combination of Illinois land records and private business documents shows. 

The price of the deal falls within a range identified as reasonable by a bank-hired appraiser. But the transaction follows similar Schock real estate deals detailed by a recent Associated Press investigation into the Illinois Republican's business transactions involving political contributors over the past decade. 

The 2014 warehouse deal, which occurred after the congressman's most recent financial report, adds to questions about Schock's pattern of reliance on campaign contributors. Political donors built, sold and financed a house owned by Schock in suburban Peoria. Donors also were involved in the sale and financing of a Peoria apartment complex in which Schock invests. 

Schock has built much of his personal wealth over a decade of real estate investments with political donors, an AP review found. Schock, 33, who was named to a midlevel Republican leadership post in the House last year, has disclosed personal wealth in a range centered on $1.4 million. He's made his precocious business acumen a key part of his appeal since his election to Congress in 2009 and sometimes describes himself as a real estate developer. A media-savvy lawmaker, he also posed shirtless for Men's Health magazine to promote fitness. 

In a separate report Monday, the website Buzzfeed reported that Schock spent more than $5,000 from his House account for a portable podium that looks a lot like a presidential podium used by President Obama. 

Rep. Aaron Schock Resigns | FindTheBest

Politico first reported the resignation on Tuesday. 

Fox News' Mike Emanuel and Chad Pergram and The Associated Press contributed to this report.