US Secretary of State John Kerry postponed a trip to Israel and Palestinian territories this week to attend White House talks on Syria amid growing calls for America to arm the opposition.

The news came as Kerry's efforts to rekindle the Middle East peace talks appear to have bogged down, and as a flow of Hezbollah fighters into Syria is helping the regime win a string of victories against the rebels.

"The secretary will be in Washington this week. He had planned a trip that was widely reported across the region," State Department spokeswoman Jen Psaki told reporters on Monday.

She confirmed Kerry would be taking part in White House meetings on Syria, describing them as "routine" talks in which President Barack Obama's national security team explores "all possible options that would accomplish our objective of helping the Syrian opposition."

But Psaki refuted the notion that Washington was getting close to bending to pressure and dropping its refusal to arm the Syrian opposition.

"There's been a long conversation about how to continue to aid the opposition and what we can do to strengthen their position on the ground while also planning a political transition. Many of these options have been discussed and they will continue to be," she stressed.

Kerry is also trying with his Russian counterpart Sergei Lavrov to organize a peace conference bringing together the regime of President Bashar al-Assad and the rebels in a bid to end the fighting that has claimed 94,000 lives.

Amid wrangling between opposition leaders and a fierce debate over exactly who should attend, the date for the talks initially slated for May has now slipped into July at the earliest.

"We have prepared a wide range of options for the president's consideration," National Security Council spokeswoman Bernadette Meehan told AFP, adding there were "no new announcements at this time."

The postponement of Kerry's Israel trip will raise fears that it could spell trouble for his peace-making efforts, even though the visit -- which would have been his fifth in four months -- had never been officially announced.

Psaki said the postponement was due to Kerry's need "to balance foreign travel and foreign diplomacy and that part of his job... with the need to be here in Washington from time to time."

She stressed, though, that he remained focused on Middle East peace efforts, offering assurances the trip would happen "soon, in the short term."

Last week, Kerry warned that if his efforts to kickstart the peace negotiations, frozen since 2010, fail there may never be another chance.

"We are running out of time. We're running out of possibilities... If we do not succeed now, we may not get another chance," Kerry told the American Jewish Community Global Forum.

He has warned leaders on both sides that they now need to take the "tough decisions" to get back to the negotiating table.

In another sign of the difficulties, Israeli Prime Minister Benjamin Netanyahu said that Palestinian preconditions made a return to negotiations impossible for Israel.

"To me, the setting of preconditions is an insurmountable obstacle," Netanyahu told the foreign affairs and defense committee.

The Palestinians say they will only return to negotiations if Israel stops building on land they want for their future state and if the Jewish state agrees to negotiate on the basis of the borders that existed before the Six-Day War in 1967.

Israel demands talks "without preconditions" and refuses publicly to freeze settlement building. But Palestinians say the Israeli demands are themselves a precondition.

Palestinian negotiator Saeb Erakat said Netanyahu was trying to paint Palestinian leader Mahmud Abbas into a diplomatic corner.

"This is the start of trying to shift responsibility for the non-resumption of negotiations to the president and the Palestinian leadership," he said in an interview.