Washington's Middle East envoy launched a new effort Thursday aimed at restarting Israeli-Palestinian peace negotiations, just as President Obama expressed pressimism about the prospects.

Already complicating envoy George Mitchell's mission was a new demand by Prime Minister Benjamin Netanyahu for an Israeli military presence in the West Bank to stop weapons smuggling, even after formation of a Palestinian state.

Mitchell met Thursday with Israeli Defense Minister Ehud Barak, Foreign Minister Avigdor Lieberman and President Shimon Peres. He was scheduled to see Netanyahu later Thursday.

As Mitchell began his mission, his boss, Obama, admitted he overreached in the Mideast.

In an interview with Time Magazine published Thursday, Obama said internal conflicts made it hard for the Israelis and Palestinians to restart talks, "and I think that we overestimated our ability to persuade them to do so when their politics ran contrary to that."

He said Israel "found it very hard to move with any bold gestures," while Palestinian President Mahmoud Abbas had "Hamas looking over his shoulder."

Obama concluded, "I think it is absolutely true that what we did this year didn't produce the kind of breakthrough that we wanted and if we had anticipated some of these political problems on both sides earlier, we might not have raised expectations as high."

Before meeting Peres, Mitchell pledged to soldier on. He said Obama's vision is a Palestinian state alongside Israel in peace. "We will pursue (that) until we achieve that objective," Mitchell said.

The envoy is set to meet with Palestinian officials in the West Bank on Friday.

Mitchell has been laboring without success for a year to get both sides back to the negotiating table, and Netanyahu's new demand made his mission even tougher.

Netanyahu said Israel must maintain a presence "on the eastern side of a prospective Palestinian state" to keep militants from using the territory to launch rockets at Israel's heartland.

The eastern side of such a state would be the part of the Jordan Valley that lies in the West Bank.

Abbas aide Nabil Abu Rdeneh rejected the demand. "The Palestinian leadership will not accept a single Israeli soldier on Palestinian land after ending the Israeli occupation," he told The Associated Press.

The Palestinians have refused to sit down with Israel until it stops all construction in the West Bank and east Jerusalem, saying it is eating up lands they claim for their future state. Israel, which captured both areas in 1967, has slowed settlement construction in the West Bank, but has applied no restrictions in east Jerusalem, which Netanyahu hopes to retain.

Israel also says negotiations should begin immediately with no conditions, but the Palestinians accuse Israel of heaping plenty of conditions of its own, including the demilitarization of a future Palestinian state, the retention of east Jerusalem and now, a military presence along Jordan's border.

The Israeli leader heads a coalition largely opposed to the sweeping territorial concessions that would be necessary to clinch a peace deal with the Palestinians. He himself had long refused to endorse the concept of Palestinian statehood, doing so only in June under intense U.S. pressure.