Responding to criticism that the conflict in Iraq is merely a civil war in a foreign country, President Bush said during a news conference at the White House on Thursday that "this notion that this isn't a war on terror is, in my view, naive."

Bush made the comment one day after 2008 Democratic presidential candidate and former U.S. Sen. John Edwards dismissed the U.S.-led war on terrorism as "a bumper sticker, not a plan."

Speaking in the White House Rose Garden, the president also stated that the upcoming summer months will be a critical time for his troop "surge" in Iraq. He indicated that the last five brigades making up the 30,000-troop buildup should arrive in Baghdad by mid-June.

"We are going to expect heavy fighting in the next weeks and months, and we can expect American and Iraqi casualties," Bush said. "We will stay on the offense," he added, repeating what has become for him a consistent refrain: "It's better to fight them there than to fight them here."

Asked how long he could sustain the policy without achieving significant progress on the ground, Bush noted that the U.S. commander in Iraq, Gen. David Petraeus, is due to report back on the effects of the new strategy by September.

In response to a reporter's question regarding making a choice between fighting al Qaeda and the war in Iraq, the president replied that "we are fighting al Qaeda ... in Iraq."

Bush also said that "the Iraqi government needs to show real progress in return for America's continued support and sacrifice. It's going to be hard work for this young government," he added.

The president called the news conference as the House prepared to vote on $120 billion legislation that would fund the war in Iraq through September. The bill significantly does not incorporate a timetable to withdraw U.S. troops, the Democratic leaders in Congress having failed to push through earlier legislation including such a provision.

The Senate is also expected to vote on the measure on Thursday, and Congress will likely send the bill to the president for his signature over the upcoming Memorial Day weekend.

Another topic addressed during Thursday's event was Iran, which has continued to build a nuclear energy program despite calls from the U.S. and other world powers to halt the process - a suspected front to develop nuclear weapons capability.

"Unacceptable" was how Bush categorized Iran's nuclear enrichment program. "Iran, with a nuclear weapon, would be incredibly destabilizing for the world," he said.

"The world has spoken and has said no nuclear weapons programs. Yet they're constantly ignoring the demands," Bush said.

To respond to the problem, the president said, "we need to strengthen our sanctions." Secretary of State Condoleezza Rice will work with European partners "collaboratively to continue to isolate that regime," he added.

Iran has stepped up the tensions with the U.S. by detaining American citizens, including Iranian-American scholar Haleh Esfandiari, arrested during a visit to Iran to see her ailing 93-year-old mother.

"Obviously, to the extent that these people are picking up innocent Americans, it's unacceptable," Bush said. "And we've made it very clear to the Iranian government that the detention of good, decent American souls ... is not acceptable behavior."

The president also discussed immigration reform, calling it "a complex issue" that would be addressed by the compromise the Senate worked out earlier this week.

"It's a difficult piece of legislation, and those who are looking to find fault with this bill will always be able to find something," he said. "But if you're serious about securing our borders and bringing millions of illegal immigrants in this country out of the shadows, this bipartisan bill is the best opportunity to move forward."

According to supporters, the legislation would tighten the borders and toughen standards for businesses hiring immigrants in an effort to make sure the employees are legal residents.

One controversial portion of the measure would create a merit-based system for future immigrants. Officials would assign more points to those with higher skills and prioritize employment over family ties.

Finally, Bush restated his confidence in embattled Attorney General Alberto Gonzales. The president said that the Justice Department is involved in "an exhaustive investigation" into issues such as whether politics played an improper role in decisions at the Justice Department. "And if there's wrongdoing, it will be taken of," he said.

The president criticized Congress' multiple hearings into the matter, which he suspected was being dragged out "for political reasons."

"As I mentioned the other day, it's grand political theater," Bush said of the dispute.

Bush asked Congress to "move expeditiously to finish their hearings and get on to the business of passing legislation."