The announcement of an early Israeli general election by Prime Minister Benjamin Netanyahu came just in time for the main evening news bulletin on Tuesday but the public was already prepared.

Last week, as Mr Netanyahu met the leaders of his coalition partners, it became clear that he did not have their support for the 2013 budget, which must be passed by the end of this year.

It includes a series of harsh austerity measures which the smaller religious parties like the ultra-Orthodox Shas and United Torah Judaism worry will hit their constituencies.

They draw support from households with large families as well as the poor and elderly, who rely on state benefits.

In his televised statement, Mr Netanyahu said that he had decided that "the good of the State of Israel requires going to elections now, as soon as possible" and that he preferred a "short election period of three months" to avoid the economy suffering from a longer period of uncertainty.

'Weak rivals'

Of course there are many reasons why such timing is also good for the prime minister.

He is riding high in the opinion polls, along with his right-wing Likud party, and currently looks set to lead the next government.

Aluf Benn, editor of the leftist Haaretz newspaper, commented that "his rivals are weak and insignificant and have not presented an alternative to his policies... Mr Netanyahu stands out as an authoritative, experienced statesman with no viable replacement".

Certainly, with the country expected to go to the polls in the second half of January, there is now little time for the Labour leader Shelly Yachimovich or the head of the centrist Kadima party, Shaul Mofaz, to surge ahead.

According to analysts, Mr Netanyahu's biggest threat comes from a man who is not head of a party at present: Ehud Olmert.

The former prime minister, who belongs to Kadima, was recently cleared of the corruption charges which led him to resign in 2009, although he was convicted of a breach of trust. He is now free to run for parliament once again, despite facing another bribery trial.

He is widely believed to be the only figure who could rally a centre-left coalition.

Mr Netanyahu will calculate that, by holding an election sooner rather than later, that possibility will be lowered.

He has lost no time in starting his campaign. In Tuesday's address, the prime minister noted that he had led "the most stable government in recent decades" over almost four years - a rare achievement in the turbulent politics produced by Israel's system of proportional representation.

While the question of peace talks with the Palestinians was barely mentioned, he emphasised his security and economic credentials, laying out the basis of his electoral agenda.

"First, we strengthened security, and this during a period in which a difficult and dangerous upheaval has raged around us in the Middle East. And second, we strengthened the economy during another upheaval, a continuing global economic crisis," he said.

Iran issue

Economic issues will be tough for the prime minister going forward. His ratings took a dive earlier this year, when he pushed through a first round of austerity measures to plug a budget shortfall.

Last year, tens of thousands of Israelis joined protests over high living costs and demanded social welfare reform. Smaller rallies have continued sporadically.

On the issue of security, Mr Netanyahu is on much more solid ground. The first challenge he identified was "to ensure that Iran will not have a nuclear bomb".

During his time in office his efforts to press for international sanctions against Tehran over its controversial nuclear programme have won the approval of the Israeli public.

"I do think Netanyahu's speech in front of the UN General Assembly was his first election speech," says the Israeli Channel 2 News political correspondent, Amit Segal, adding that the prime minister wants "the Iran subject to be the centre of public debate".

In his comments to the UN, Mr Netanyahu called for a "clear, red line" to stop Iran from being capable of producing a nuclear weapon. He claimed that line, representing 90% of the way to making a warhead, would be reached "by next spring, at most by next summer".

By bringing forward a general election, it could be that Mr Netanyahu hopes to renew or increase his mandate before any possible attack on Iran.

Another factor in the timing of his vote could be the US presidential election. The Israeli prime minister is said to worry that if President Barack Obama is re-elected in November then tensions between them will increase because of his perceived support for the Republican candidate, Mitt Romney.

Clearing the hurdle of a national election would help remind Israel's most important ally that he remains popular at home.

The Knesset will convene for its winter session on 15 October and is expected to take a vote soon afterwards to dissolve itself.

At that point the voting date will be set. Israeli law determines that it must be a Tuesday, making 15, 22 or 29 January possible election days.