Walter Shaub Jr., Director of the US Office of Government Ethics, announced his resignation following a rocky relationship with President Trump and repeated confrontations with the administration.

Shaub did not specify a reason for his resignation in a letter to President Trump, which he released on Twitter on Thursday, the Los Angeles Times reported.

He, however, told the Washington Post he was not leaving under pressure.

Shaub, appointed by former US President Barack Obama in 2013, had unsuccessfully pressed Trump to divest his business interests to avoid potential conflicts of interest, something Trump refused to do.

The ethics watchdog also engaged in a public battle with the White House over his demands for more information about former lobbyists and other appointees who had been granted waivers from ethics rules. After initially balking, the White House eventually released the requested information about the waivers.

Shaub called for a harsher punishment for presidential advisor Kellyanne Conway after she flouted ethics rules by publicly endorsing Ivanka Trump’s clothing line during a television appearance.

In a separate statement, he said that his time working with the Trump administration made it “clear to (him) that we need improvements to the existing ethics program”.

Shaub’s resignation, effective July 19, comes nearly six months before his term expires in January. He will join the nonpartisan Campaign Legal Center as senior director for ethics.

In his letter of resignation to the President, Shaub said the office was “committed to protecting the principle that public service is a public trust”, and employees must place loyalty to ethics over private gain.

Shaub had come under fire from Trump supporters for being politically motivated and some had called for his resignation.