TEL AVIV, ISRAEL -- Israeli Prime Minister Benjamin Netanyahu has appointed a new media adviser who has tweeted critically against U.S. President Joe Biden, the daily Haaretz reported.

The appointment comes at a time when U.S.-Israel relations are strained.

Gilad Zwick, a journalist with a conservative Israeli TV station, has in his tweets called Biden "unfit" to rule and said that he was "slowly but surely destroying America." He also posted tweets suggesting he supported President Donald Trump's false claims that the 2020 U.S. election was rigged. At least one of the tweets that was live earlier was deleted later in the day.

Zwick did not respond to a request for comment but tweeted on Monday in English that he was a private citizen when writing the posts about Biden.

"I don't hold those views today and I will act in a completely professional manner in the prime minister's office," he said.

Zwick had previously worked for Israel Hayom, a pro-Netanyahu daily. Netanyahu's office declined to comment.

Zwick's appointment comes as ties between Israel and its closest ally, the United States, are fraught over a contentious Israeli government plan to overhaul the judiciary and over the government's ultranationalist character.

Biden has publicly expressed concern over the Netanyahu government's plan to reshape the legal system, which has sparked mass protests that continue weekly even after the plan was put on hold.

The Biden administration has also voiced unease about Netanyahu's government, made up of ultranationalists who were once at the fringes of Israeli politics and now hold senior positions dealing with the Palestinians and other sensitive issues.

Amid the tensions, Biden has so far denied Netanyahu a typically customary invitation to the White House after his election win late last year.

Critics accuse Netanyahu of gradually shifting Israel from a bipartisan matter to a wedge issue in U.S. politics. They point to him appearing to openly support Republican candidates as well as his 2015 speech to Congress which was seen as a slight to the Obama administration over its nuclear deal with Iran. Netanyahu says Israel's bond with the U.S. is unbreakable and downplays any rifts as disagreements between friends.

Last month, Israel's parliament hosted U.S. House speaker Kevin McCarthy, who became just the second House speaker to address the Knesset, after Republican Newt Gingrich in 1998.