FACTBOX: U.S. commander's plan to halt Iraq withdrawals

(Reuters) - Gen. David Petraeus, the top U.S. commander in Iraq, said on Tuesday the United States would stop withdrawing troops from the war zone after July to assess security conditions.

Here are highlights of testimony delivered by Petraeus and U.S. Ambassador to Iraq Ryan Crocker to Senate committees.

* The U.S. military will complete the withdrawal of about 20,000 combat troops through mid-July. But then withdrawals will stop for a 45-day assessment period, Petraeus said. After that, commanders will start a second evaluation period of to determine whether security conditions would allow Petraeus to recommend a further troop reduction.

* Petraeus, pressed by a senator, said he could not estimate how many troops might be in Iraq at the end of 2008. The United States has 160,000 troops there now.

* The "surge" of about 30,000 additional troops into Iraq last year has improved security, but those gains are "fragile and reversible," according to Petraeus and Crocker.

* The number of high-profile attacks increased in March due to activity by al Qaeda in Iraq, but the number of attacks is still far below that of a year ago, Petraeus said.

* While the surge had met the aim of creating enough calm to allow Iraqi factions to move toward reconciliation, the Iraqi government has not fulfilled all of the political objectives laid out by President George W. Bush when he announced the strategy in 2007, the officials said.

* Petraeus said withdrawing too many forces too quickly could jeopardize progress made during the surge.

* Petraeus and Crocker charged Iran, Syria and Lebanon's Hezbollah of fueling recent fighting in Baghdad, saying Tehran and Damascus were pursuing a "Lebanization strategy" in Iraq.

(Reporting by Kristin Roberts, Editing by Chris Wilson)