BAGHDAD — Sen. John McCain's trip to Iraq, which began yesterday in Baghdad, coincides with a number of milestones.

The Iraq war, to which the probable Republican presidential nominee has linked his political future, will be 5 years old Thursday. Around that date, the U.S. military is likely to suffer its 4,000th death in the war. And McCain's arrival yesterday coincided with the 20th anniversary of a chemical weapons attack in northern Iraq.

McCain met with Deputy Prime Minister Barham Saleh and planned to meet with Gen. David Petraeus, the top U.S. commander in Iraq, according to the U.S. Embassy. Further details of McCain's visit, which had been anticipated, were not being released for security reasons, the embassy said.

Before leaving the United States, McCain, one of the foremost proponents of the March 2003 U.S.-led invasion, said the trip to the Middle East and Europe was for fact-finding purposes, not a campaign photo opportunity.

But he expressed worries that militants in Iraq might try to influence the November general election.

"Yes, I worry about it," he said, responding to a question during a campaign appearance in Pennsylvania. "And I know they pay attention, because of the intercepts we have of their communications."

McCain, the senior Republican on the Senate Armed Services Committee, was accompanied by Sens. Joe Lieberman, an independent from Connecticut, and Lindsey Graham, R-S.C., two top supporters of his presidential ambitions.

The weeklong trip will take McCain to Israel, Britain and France, and include his first meeting with British Prime Minister Gordon Brown.

He also is expected to meet with French President Nicolas Sarkozy, Israeli Prime Minister Ehud Olmert and other Israeli officials.