The rightwing Israeli opposition leader, Binyamin Netanyahu, today appeared increasingly likely to become the country's next prime minister after winning the key endorsement of a far-right politician.

Avigdor Lieberman, whose party, Israel Our Home, came a strong third in last week's general elections, met the Israeli president, Shimon Peres, and told him he would support Netanyahu to lead a new coalition government.

He said he preferred to see Netanyahu lead a broad, national unity government but added that he would join even a narrow rightwing cabinet.

Even though Netanyahu, leader of the Likud party, came a close second in the elections, he has been favoured to become prime minister because the success of other rightwing parties means he could put together a majority coalition government far more easily than his rival Tzipi Livni.

Livni, the foreign minister and Kadima party leader, won the vote by just one seat.

She took 28 seats, just ahead of Netanyahu on 27.

Lieberman won 15 seats, turning him effectively into a kingmaker, but – as expected – no one party came anywhere close to a majority in the 120-seat Knesset, meaning the next prime minister would again have to rely on a coalition.

Yesterday, Peres began discussions with all the elected parties and, based on their recommendations, will choose which MP will be given the chance of forming a coalition and becoming prime minister.

A new government is not likely to be established for at least another month.

The Ha'aretz newspaper website quoted Lieberman as telling Peres that he saw three possibilities: "A broad government, which is what we want.

"A narrow government, that will be a government of paralysis, but we don't rule out sitting in it. And the third option is going to elections, which will achieve nothing."

Two smaller rightwing parties have said they will endorse Netanyahu. He is expected to win the support of others, which should give him at least a 65-seat coalition.

The key question now will be whether he can convince Livni and her Kadima party to join his government to provide it with more stability.

Livni has argued that, since she won the election, she should become the prime minister, and it is not clear if she would serve under a Netanyahu leadership.

Some in her party said they would prefer to go into opposition, although Kadima, which is barely three years old, has never been in opposition before.

Two possible Livni allies, the Labour party and the leftwing Meretz party, said they would not offer any endorsement for prime minister, which undermined her chances even further.

Ehud Barak, the current defence minister and head of Labour, said his party was heading into opposition.

"Our only option is to refrain from recommending anyone," he told a party meeting.

"The picture is clear, and we are going to the opposition. In this reality, in my opinion, there is just one possibility – not to recommend any of the candidates for prime minister."

Peres was due to finish consulting with party leaders later today, and will then announce who will be given the chance to form the next government.

The US Senator John Kerry and two Democratic congressmen, Brian Baird, of Washington, and Keith Ellison, of Minnesota, were due to travel to Gaza today to see the situation there for themselves after Israel's war last month.

They were to meet UN officials, but no meetings with any Hamas figures were scheduled. It follows a visit by a group of British Labour party MPs earlier this week.