WASHINGTON, July 21 (Reuters) - Attacks in Iraq last month reached their highest daily average since May 2003, showing a surge in violence as President George W. Bush completed a buildup of U.S. troops, Pentagon statistics show.

The data, obtained by Reuters from the Defense Department, showed an upward trend in daily attacks over the past four months, when U.S. and Iraqi forces were ramping up operations against insurgents and militants, including al Qaeda, in Iraq.

Pentagon officials were not immediately available to comment on the statistics.

The June numbers showed 5,335 attacks against coalition troops, Iraqi security forces, civilians and infrastructure.

June's total was 2.5 percent below an October 2006 peak of 5,472 attacks and slightly lower than the 5,365 attacks in May.

But because June has only 30 days, the average daily number of attacks was 177.8, higher than the 176.5 last October and 173.1 in May.

The Pentagon statistics, which come as pressure mounts in the U.S. Congress for a troop withdrawal from Iraq, depicted the most intensive month for daily attacks since Bush declared major combat operations at an end in May 2003.

Daily attacks rose as the Bush administration moved the last combat battalions into place for a security clampdown in Baghdad, part of a controversial U.S. strategy to stabilize Iraq with an additional 28,000 troops.

Bush and other senior officials have predicted that a rise in violence from insurgents and al Qaeda in Iraq would occur this summer as the so-called "surge" strategy takes hold.

A crucial report expected in September from U.S. Ambassador to Iraq Ryan Crocker and the top U.S. commander in Iraq, Gen. David Petraeus, could force a change in U.S. policy if it suggests the strategy is not working.

U.S. military commanders have sought to paint a more upbeat picture of events on the ground while pleading for additional time to determine whether the Bush strategy can succeed.

The statistics showed the 177.8 attacks per day in June were above the 157.5 in March, the lowest daily average for any month in 2007. Total monthly attack figures have also climbed to well over 5,000 from a low in February of 4,561.

Attacks last month were up 46 percent from a year earlier, with the statistics showing 3,642 attacks or 121.4 per day on average in June 2006.

The June 2007 statistics confirmed a significant decline in the targeting of Iraqi civilians, with such attacks falling 18 percent to 763 from a 2007 high of 932 in May.

Attacks on Iraqi security forces fell to 889 in June from 987 in May, while attacks on coalition forces rose about 7 percent to 3,671 from 3,423.