Kerry filed a complaint on Friday against the pro-Bush group Swift Boat Veterans for Truth, which has questioned the Democratic challenger's military record and replaced the Iraq conflict with the Vietnam war in the minds of many Americans.
The White House has consistently denied any link between Bush's campaign and Swift Boat Veterans for Truth. The administration has said it respected Kerry's wartime service, but refused categorically to repudiate the charges against him.
The Kerry campaign said it had "filed a legal complaint against Swift Boat Veterans for Truth (SBVT) before the Federal Election Commission (FEC) for violating the law with inaccurate ads that are illegally coordinated with the Bush-Cheney presidential campaign".
SBVT spokesman John O'Neill dismissed the complaint as "completely frivolous".
It remained unclear whether Kerry's surprise legal action would force the SBVT, which unleashed a second television commercial against Kerry on Friday, to withdraw that advertisement as well as a first advertisement released in early August.
The advertisement itself has come under criticism, with observers pointing out inconsistencies and faults in the group's allegations.
Kerry, who won five medals as a gunboat commander in the war, has used his combat exploits to tout his national security credentials in the first presidential campaign since the 11 September 2001 attacks.
However, there are signs that the group's first advertisement -shown in select states but enjoying national media coverage - has taken its toll on his support among fellow veterans he hoped would help him win the 2 November election.
Polls suggest support for Kerry
among veterans has dipped
The Kerry campaign statement cited recent press reports about the group and public statements by some of its members to buttress its claim of improper ties to the Republican party and Bush's campaign.
The New York Times on Friday reported there was a "web of connections" between the SBVT and the "Bush family, high-profile Texas political figures and President Bush's chief political aide, Karl Rove".
White House denial
The White House denied again on Friday that it had any connection to the Swift Boat group and accused Kerry of "losing his cool".
"We've already said we weren't involved in any way in these ads. We've made that clear," White House spokesman Scott McClellan said in Crawford, Texas, where Bush is on vacation at his ranch.
Kerry won three Purple Hearts for wounds suffered in combat and a Bronze Star and a Silver Star for bravery, and points to his navy record as evidence that he served with distinction.
"Thirty years ago, this was the plain truth. It still is. And I still carry the shrapnel in my leg from a wound in Vietnam," the Massachusetts senator told a firefighters' union.