Army Radio, which aired what it said were comments he made on Monday to activists of his right-wing Likud party, interpreted them as referring to foreign funding for advocacy groups campaigning for a change of government in Israel.
Political parties in Israel are banned from accepting money directly from overseas donors during an election campaign. But such funding is allowed under Israeli law for non-profit organizations espousing political viewpoints, and US consultants have advised Israeli candidates for years.
"It is a very tight race. Nothing is guaranteed because there is a huge, worldwide effort to topple the Likud government," said Netanyahu, who received rousing applause in the US Congress last week during a speech against a potential nuclear deal with Iran sought by the administration of President Barack Obama.
The visit came at the invitation of the Republican leadership of Congress, angering the White House and Democratic legislators. Critics accused Netanyahu of intervening in US politics, and the Republicans of trying to boost his re-election prospects.
Likud and the centre-left Zionist Union are running neck-and-neck in opinion polls ahead of the March 17 ballot, with Netanyahu widely seen by political commentators as having a better chance of forming a governing coalition after the vote.
As election day approaches, "Netanyahu is feeling the pressure ... he is shooting in all directions", Zionist Union leader Isaac Herzog told Israel Radio.
Defense Minister Moshe Ya'alon echoed the prime minister's sentiments and said Sunday that "English-speakers" were scheming to promote left-wing and Israeli Arabs to go out and vote come Election Day.
"There are non-profit organizations here that are funded by foreign money – European money and other groups that don't want to see Netanyahu (in power)," said Ya'alon at an event at the Interdisciplinary Colledge in Herzliya.