The roundups were part of two entirely different counterterrorism cases under investigation by French judges, and fell on the same day only by coincidence, one police official in Paris said.
Firearms were seized in one of the sweeps, another official said.
The arrests come as France and many other European nations have stepped up terrorism alert vigilance amid what has been described as an abstract though heightened threat in recent weeks. The U.S. government warned Americans over the weekend to use caution when traveling in Europe.
In one of the cases, nine suspected Islamic militants were detained in southeastern Marseille and its suburbs, and authorities turned up at least one automatic rifle and a pump gun, the officials said.
In Tuesday's other roundup, two men were arrested in Marseille and another in southwestern Bordeaux on suspected ties to a Frenchman arrested in Naples, Italy, last month accused of links to an Afghan recruiting ring.
"This very morning, police operations were launched in Marseille and Bordeaux that led notably to three arrests directly linked to the fight against terrorism," Interior Minister Brice Hortefeux said during a question-and-answer session in parliament's lower house.
He made no reference to the nine other arrests.
Asked about the U.S. travel advisory, Hortefeux said France "has been very attentive and has heard the advisory by American authorities to their nationals" and noted France's strong cooperation with its allies.
A third police official said agents from counterterrorism agency DCRI had detained the suspects in Marseille and Bordeaux over suspected links to a group offering lodging and fake identity papers to Islamic militants looking to come to France.
The three men were alleged accomplices of a Frenchman detained in Naples last month and suspected of having fought in Afghanistan.
Italian newspapers reported that the man was 28 years old, of Algerian origin and suspected to be a member of al-Qaida.
The DCRI has been leading an investigation of a suspected feeder network of militants headed to the border region between Afghanistan and Pakistan, where Western authorities believe that Osama bin Laden is hiding and which has been a key zone of operation from fighters from Afghanistan's former Taliban regime.
Domestically, President Barack Obama's press secretary, Robert Gibbs, emphasized that Americans were not being told to stay home.
Obama was briefed on the situation Saturday, Gibbs told reporters. On Sunday, the U.S. issued an alert to Americans living in or traveling to Europe to be vigilant because of the threat of terrorism there.
"We are concerned enough to alert those who are in Europe to be alert to their surroundings," Gibbs said at a White House briefing. People should be alert to suspicious activities and should be aware of where to go in an emergency, he said.
,p> Earlier, officials with the FBI and the Homeland Security Department said they had have no indication that terrorists were targeting the U.S. or its citizens as part of a new threat against Europe.According to an intelligence bulletin obtained by The Associated Press, the FBI and Homeland Security said they believe the al-Qaida terrorist network continues to want to attack the United States but that there is nothing pointing to anything specific, imminent or related to the European plots. They warned law enforcement authorities to be on the lookout for suspicious activity, as it's more difficult to detect terror plots carried out by individuals or small groups.
"We are aware of, and closely monitoring, recent reporting indicating a terrorist threat to Europe," the bulletin said. "At this time, there is no indication that the reported threat is directed specifically toward the United States, its citizens or infrastructure; however, we assess that al-Qaida and its affiliates continue to plot against the homeland and U.S. allies."
Amtrak will be increasing security beginning Friday for a planned exercise that is not related to the Europe threat, a Homeland Security official said. The official spoke on condition of anonymity to discuss the exercise because it hasn't started yet.
The exercise, known as operation RAILSAFE, often takes plan over holidays when rail travel is up.
Meanwhile, German officials are being tightlipped about details surrounding a U.S. missile strike in Pakistan's rugged mountain border area that Pakistani officials say killed five German militants.
U.S. officials believe a cell of Germans and Britons at the heart of the terror alert for Europe - a plot that U.S. officials link to al-Qaida leader Osama bin Laden - are believed to be hiding in that region.
German public television ARD cited unnamed sources Tuesday as saying that four German citizens of Turkish descent were killed in the missile attack.
Germany's Foreign Ministry said late Monday it was investigating the reports, but did not return calls seeking comment Tuesday on the militants' identities.
The U.S. State Department alert Sunday advised the hundreds of thousands of American citizens living or traveling in Europe to take more precautions about their personal security. The Japanese alert was similar.
Britain's Foreign Office warned travelers to France and Germany that the terror threat there was high. Sweden's Foreign Ministry did not single out any particular countries in its message.
Amid increased security in Paris, 61 soldiers from an Alpine regiment were deployed over the weekend at two sites in Paris, Notre Dame Cathedral and the Sacre-Coeur Basilica, the joint staff of the Paris defense zone said.
One trigger for the heightened concern came from French authorities last month. A parade of officials said France was facing its highest terror alert level in years, pointing to increased violence and threats by al-Qaida's North African branch.
The public concerns intensified last week after a Pakistani intelligence official said eight Germans and two British brothers were at the heart of an al-Qaida-linked terror plot against European cities.
Security officials say terrorists may be plotting attacks in Europe with assault weapons on public places, similar to the deadly 2008 shooting spree in Mumbai, India. European officials have provided no details about specific targets.
ABC News reported that one scenario authorities fear is a repeat of the 1985 attack on the Rome and Vienna airports, when Palestinian extremists threw grenades and opened fire on travelers waiting at ticket counters injuring 140 and killing 19, including a small child.
A curfew was ordered this weekend at Ramstein U.S. Air Force Base in Germany, with soldiers told to remain at home and not to wear uniforms off base "in response to a threat condition," a Ramstein spokesperson said. The U.S. European Command (EUCOM) commented, "With the increased reports of terror activity throughout Europe, the US and its allies are working to ensure the safety and security throughout the region. The US and partner nations are working to investigate and prevent possible terror threats."
But despite public alerts, there are still concerns the terror group may go ahead with attacks.
CLICK HERE TO FOLLOW ABC NEWS COVERAGE ON THE BLOTTER
Information from ABC News and The Associated Press included in this report.
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