Richard Grenell, a vocal loyalist of US President Donald Trump, has officially resigned as US envoy to Germany, capping a contentious two-year tour of duty in Berlin that sparked transatlantic frictions.

In February, Grenell, a prominent figure in Republican spheres and one of the most notable gays in the Trump administration, had been chosen to temporarily head the US intelligence.

Based on a report by the German Press Agency, Grenell's deputy Robin Quinville would replace him as ambassador on an interim basis, Giordono-Scholz disclosed. Quinville has been deputy chief of mission at the German consulate since July 2018.

The 53-year old Grenell aroused quite a bit of controversy and made few friends in Germany's political circles during his two-year stint. He vigorously pursued the foreign policy agenda of Trump in ways that were often seen as intruding as an ambassador beyond his diplomatic functions.

Grenell posted the news on his Instagram account late Monday, without elaborating his next plans. While no reason was disclosed why he quit, many speculate Grenell may join Trump's re-election campaign.

Trump appointed Grenell as official envoy to Germany in April 2018. He regularly drew the ire of politicians in Germany with criticism of almost everything -- from the Iran nuclear agreement to Berlin's defence budget and ties with Chinese tech giant, Huawei.

He made headlines with his strong views, often expressed through social media, although officials in the country largely held back criticism of Trump's chosen official.

Grenell had already indicated that he would not be coming back to Germany as soon as the non-permanent function in Washington is over. He will continue his role as US ambassador for the Kosovo-Serbia negotiations.

Last year, Grenell treaded into the sticky issue of Berlin's Nord Stream 2 gas project with Russia, writing letters to German firms that are involved in the venture in January stating they risk being penalized by Washington.

Trump approved a Senate legislation in 2019 that allowed sanctions against companies involved with the equipment laying the pipeline under the Baltic Sea.

Grenell also threatened the US could restrict intelligence sharing between Germany and the US if German officials allowed Huawei to take part in the country's 5G network program.

Grenell's stint as acting chief of national intelligence did not sit well with Democrats who claimed he lacked the necessary experience for the job. Meanwhile, it is being speculated that Grenell may be given a top role by Trump on his re-election campaign.