Benjamin Netanyahu, the Israeli prime minister, is heading to Washington for talks with President Barack Obama which will focus on Iran's diplomatic charm offensive.

I will speak the truth. Facts must be stated in the face of the sweet talk and the blitz of smiles

Benjamin Netanyahu, Israeli PM

While Obama will attempt to reassure Netanyahu that he will not act prematurely to ease sanctions on Iran, growing signs of a US-Iranian thaw have rattled Israel and could make for a tense encounter between the two leaders.

Netanyahu, who will meet Obama at the White House on Monday then address the UN on Tuesday, said he would "tell the truth in the face of the sweet talk".

"I will speak the truth. Facts must be stated in the face of the sweet talk and the blitz of smiles," Netanyahu said at the airport in Tel Aviv before departing for the United States.

Before leaving the US on Friday, Iran's new President, Hassan Rouhani, shared a 15-minute phone call with President Obama, during which he said he wanted to seek a deal with world powers on Iran's nuclear programme within months.

The conversation was the highest-level contact between the two countries for more than 30 years - fuelling hopes for a resolution of a decade-old Iranian nuclear standoff.

Israeli scepticism

Israel and the West suspect Iran is trying to build a nuclear bomb. Tehran denies the claim.

On his return to Tehran on Saturday, Rouhani was welcomed by hundreds of supporters hailing his trip [AFP]

"Netanyahu does not care that he is the only one ruining the party," an Israeli official said.

Obama is expected to voice sympathy for Israel's scepticism about Iran, its arch-foe, but will make clear his determination to test Rouhani's intentions and will press Netanyahu for time to do so, US officials say.

For his part, Netanyahu will tell Obama that tough economic sanctions have succeeded in forcing Iran back to the negotiating table and "they should not be eased, quite the contrary, they should be tightened," a second Israeli official said.

Netanyahu will urge Obama to reject any deal that calls for concessions by the West and instead demand specific steps by Iran, including shutting down their uranium enrichment and plutonium projects and shipping out their fissile material stocks.

"He will tell the president 'better no deal than a bad deal,'" the official said.

The Obama administration has been vague on exactly what concessions it wants from Iran, and a source close to the White House said the president is expected to resist the Israeli pressure for a precise time limit for diplomacy to produce an agreement.

Source: Al Jazeera and agencies