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Israeli Prime Minister Binyamin Netanyahu has given a rare and unscheduled television interview to combat allegations of improper behaviour from his rivals before the April elections.

Saturday night's interview with Channel 12 came just before he boarded a plane for Washington, where he was due to meet US President Donald Trump and address the annual conference of the American Israel Public Affairs Committee (AIPAC), a pro-Israel lobby.

The prime minister walked into the studio while the anchors, notified only a short while before, were presenting the evening news.

Netanyahu, already under threat of indictment for separate corruption allegations, has come under renewed scrutiny in recent days over his handling of submarine deals.

His electoral opponents have repeatedly suggested that Netanyahu may have benefited financially from them - which the prime minister says is completely false. 

"I have to smash the wave of lies spread by (Benny) Gantz and (Yair) Lapid and (Moshe) Yaalon and (Gabi) Ashkenazi," Netanyahu said of the leaders of the centrist Blue and White electoral alliance.

The four say Netanyahu may have pushed for an unnecessary submarine acquisition from Germany's Thyssenkrupp to boost the stock of a company in which he had owned shares.

Blue and White also claim Netanyahu could have committed treason by agreeing to allow Germany to sell Egypt submarines without the knowledge of the defence ministry.

Germany consults with Israel before such sales due to the relationship between the two countries, Israeli media has reported.

Netanyahu said on Friday he was suing his opponents for libel, but arrived at the television studio nonetheless to defend himself.

At the advice of his cousin, Netanyahu had in 2007 bought $600,000 of stock in a company that manufactured components used in the metal industry, he said.

He said he sold it in 2010 - when already premier - and that the relevant authorities were made aware of the holdings and sale.

He reportedly sold at a profit of more than $3 million.

Netanyahu added that the submarine sale to Israel took place over a year after he no longer held stock.

"It's a company that has nothing to do with submarines," he said.

The claim that he compromised Israel's security by allowing Germany to sell Egypt submarines was "a blood libel", Netanyahu said.

He said the reasons he agreed to it were "secret" due to state security, but noted the head of the national security council and attorney general were aware.

Police have investigated the submarine acquisitions and recommended pressing charges against a number of people involved, including Netanyahu's cousin and lawyer David Shimron. 

Netanyahu was questioned as a witness in the case and was not considered a suspect.

Netanyahu claims unfair treatment from the mainstream Israeli media and has largely refrained from studio interviews.

He has instead been using his "Likud TV" internet broadcasts and social media as a means to spread his messages ahead of the April 9 general elections.