Secretary of State Condoleezza Rice returned to Israel on Sunday for the third time in six weeks, seeking to nudge the Israeli and Palestinian sides before an upcoming U.S.-sponsored peace conference.

But after a day of meetings with Israeli officials, including Prime Minister Ehud Olmert, Rice acknowledged that her two-day visit was unlikely to get the two sides to agree on the joint pre-conference statement of goals that the U.S. has sought.

"They're still working. And like with anything of this kind, you know, they're going through some knotty discussions," Rice said. "I think those knotty discussions are going to continue for a while, but I will go out and see if there is anything that I can do to help move this along."

The conference is scheduled to take place before Dec. 21, but no formal date has been set and Rice said the time wasn't right yet to issue formal invitations.

Rice was scheduled to meet today with Palestinian President Mahmoud Abbas.

Negotiating teams, led by former Palestinian Prime Minister Ahmed Korei and Israeli Foreign Minister Tzipi Livni, remain at odds over the statement of goals. Palestinian officials have pressed for inclusion of specific issues such as right of return for Palestinian refugees and the borders of a Palestinian state.

Rice has supported the Israeli preference for a more vague document with no set timelines.

"It is not true that Israel is avoiding in advance discussion of the sensitive issues," Livni said. "We must see if it is possible to reach understanding on these topics, to see if we can proceed."

Livni said Israeli security concerns must be addressed. But she praised Abbas' government as a serious negotiating partner, in contrast with the militant group Hamas, which controls the Gaza Strip.

"The bad news is, terrorism rules in Gaza," Livni said. "The good news is, there is a moderate Palestinian leadership that accepts the idea of peace, the vision of two states living in peace and security."

In Gaza, Israeli airstrikes killed four Palestinians. Rockets fired by Palestinian militants knocked out power to 300 homes in the Israeli city of Sderot.