WASHINGTON (Reuters) - U.S. Defense Secretary Robert Gates said on Sunday he was disappointed with the Iraqi government's lack of significant progress and said the nation's parliament should not have taken a summer break.

He said he had urged the parliament not to recess while U.S. troops were fighting in intense summer heat, trying to buy time for Iraqi political leaders to resolve their differences.

"I said 'for every day that we buy you, we're buying it with American blood. The idea of you going on vacation is unacceptable,'" he said on NBC's "Meet the Press."

Iraq's parliament recessed this week for the month of August, the same week the main Sunni bloc quit Prime Minister Nuri al-Maliki's Shi'ite-led government.

The Iraqi government is under pressure to reach a power sharing deal with the country's divided sects, as well as to pass key laws for fair distribution of oil revenues, readmit former members of Saddam Hussein's Baath party to civil service and set a date for provincial elections.

"The disappointing part of this, of course, is the lack of significant progress at the national level and the Sunni withdrawal from the government," said Gates on CNN's "Late Edition."

Gates was speaking just days after visiting Egypt and Saudi Arabia with U.S. Secretary of State Condoleezza Rice.

Gates said a reduction in the 155,000-strong US force in Iraq by the end of this year was "a possibility"

Gates said the US "surge" troop hike had succeeded in dampening violence and that progress was being made in places like Al-Anbar province, where he said Sunni former opponents of the US occupation have switched to the US side recent months.