Washington (CNN) A defiant Sen. Robert Menendez asserted his innocence and pledged to fight federal corruption charges brought against him Wednesday, which he said were politically motivated and "intended to silence me."

"I have always conducted myself in accordance with the law. I have always stood up for what I believe is right. I fight for issues I believe in the people I represent and the safety and security of this country every single day. That's who I am and I am proud of what I have accomplished and I am not going anywhere," he said during a press conference Wednesday evening.

The case, brought by the Justice Department's public integrity unit, sets up a high-stakes battle between a New Jersey senator who has fought off investigations for years, and federal prosecutors and the FBI who have spent years pursuing him.

In a video to supporters posted Thursday on YouTube, Menendez called that three-year inquiry and his indictment a failure of justice, but said he took it as an opportunity.

"That failure affords me the opportunity to finally show beyond a doubt that the charges leveled today and through a nearly 3 year campaign of innuendo and smears are completely false," he said in the video.

Menendez conceded in the Thursday video that "today is a difficult day," but said he is "strengthened by the unwavering support of so many people across New Jersey and across the usual partisan lines."

Menendez agreed to temporarily step aside as top Democrat on the Senate Foreign Relations Committee, according to a Senate Democratic aide.

But he pledged to remain in office on Wednesday, and said that he began his career fighting corruption and "this is not how my career is going to end."

"I'm angry and ready to fight because today contradicts my public service career and my entire life," Menendez said.

He charged that prosecutors "don't know the difference between friendship and corruption and have chosen to twist my duties as a senator and my friendship into something that is improper."

"They are dead wrong."

JUST WATCHED Feds preparing corruption charges against Democrat sen. Replay More Videos ... MUST WATCH Feds preparing corruption charges against Democrat sen. 01:55

"Robert Menendez, a U.S. senator, and Dr. Salomon Melgen, a Florida ophthalmologist, were indicted today in connection with a bribery scheme in which Menendez allegedly accepted gifts from Melgen in exchange for using the power of his Senate office to benefit Melgen's financial and personal interests," said Peter Carr, a Justice Department spokesman, in a statement.

The two were indicted in the district of New Jersey for one count of conspiracy, one count of violating the travel act, eight counts of bribery and three counts of honest services fraud; Menendez was also charged with one count of making false statements, according to Carr's statement.

Federal officials and Menendez's attorneys had discussed plans for the New Jersey Democrat to turn himself in before a planned court hearing on Thursday, according to people briefed on the case.

Menendez has not turned himself in yet, according to Steven Sandberg, his press secretary, and he does not know if he will do so Wednesday night or Thursday morning. ​

The government's case, as first reported by CNN last month , centers on Menendez's relationship with Melgen, who the senator has called a friend and political supporter. Melgen and his family have been generous donors to the senator and various committees the senator is associated with.

Investigators have focused in part on plane trips Menendez took in 2010 to the Dominican Republic as a guest of Melgen. In 2013, after word of the federal investigation became public, Menendez paid back Melgen $58,000 for the 2010 plane trips calling his failure to properly disclose the flights an "oversight."

"Government corruption -- at any level of elected office -- corrodes the public trust and weakens our democratic system," said Assistant Attorney General Caldwell.​

Richard Frankel, who head the FBI's New Jersey office, said: "The citizens of New Jersey have the right to demand honest, unbiased service and representation from their elected officials at all levels of government. The charges and activity alleged in this indictment are another example of the FBI's commitment to aggressively and tenaciously pursue public corruption in the state of New Jersey."

Menendez has said he's innocent, noting that he has been friends with Melgen for more than 20 years and that the two families have spent holidays and other special occasions together.

After CNN reported on the pending charges, Menendez told reporters that he has "always conducted myself appropriately and in accordance with the law. And I am not going anywhere."​

One of the highest-ranking Hispanic members of Congress, Menendez is a former chairman of the Senate Foreign Relations Committee. He has become one of the Obama administration's most vocal Democratic opponents on two key foreign policy matters -- President Barack Obama's decision to ease the trade embargo against Cuba and also his effort to engage direct negotiations with Iran over that country's nuclear program.

Prosecutors were under pressure in part because of the statute of limitation on some of the allegations. Attorney General Eric Holder signed off on the plan to bring charges and had expected to be gone by the time they were announced. However, an unrelated political fight over abortion in the Senate has stalled the nomination of Holder's successor, Brooklyn U.S. Attorney Loretta Lynch.

This is the first indictment of a sitting senator since the prosecution of Ted Stevens, whose conviction the Justice Department tossed out because of prosecutor misconduct in the case.

It poses a high-profile test of the Justice Department's ability to prosecute sitting lawmakers, having already spawned a legal battle between prosecutors and Menendez's attorneys over whether key evidence the government has gathered is protected by the Constitution's Speech and Debate clause