Updated, 5:06 p.m.

U.S. citizens have been taken hostage by an extremist group out to avenge the French offensive against Islamist fighters in Mali, an unforeseen consequence of the operation that could get the U.S. involved directly in the conflict.

State Department spokeswoman Victoria Nuland confirmed on Wednesday that an unspecified number of American citizens were abducted by an Islamist militant group at an eastern Algerian oil field early in the day. A group claiming responsibility for the abduction, Katibat Moulathamine, or the "Masked Brigade," told a Mauritanian news service that the abduction was a retaliation for the French air campaign against Islamist militants in northern Mali, begun on Friday. With the caveat that early reports are often mistaken, ABC News reports that the attackers are believed to be affiliated with al-Qaida.

At the Pentagon, officials learned about the abduction of U.S. citizens Wednesday morning. A response has yet to be formulated. "We're tracking the situation closely, and there's no planned response at this point, but we're assessing," says Maj. Rob Firman, a Pentagon spokesman.

A spokesman for the U.S. Africa Command, the U.S. regional command responsible for military operations on the continent, referred questions to the State Department. Secretary of Defense Leon Panetta, traveling in Europe on Wednesday, called the abduction a terrorist act and said the U.S. would take "all necessary and proper steps" to respond, according to Julian Barnes, a Wall Street Journal reporter traveling with Panetta.

BP, the oil company operating at the In Amenas oil field, released a statement saying the site was "attacked and occupied by a group of unidentified armed people." The company's understanding is that the occupation is ongoing. "We do not yet have confirmed information on the status of personnel at the site but believe some are being held by the occupiers," BP stated.

Oil Company BP's map of its operations in Algeria. U.S. citizens were among the hostages taken at the In Amenas oil field on Wednesday. Graphic: BP Oil Company BP's map of its operations in Algeria. U.S. citizens were among the hostages taken at the In Amenas oil field on Wednesday. Graphic: BP

The U.S. has yet to get involved in the French effort in Mali, now in its sixth day. Since France began its air campaign, Pentagon officials have suggested that they would likely provide the French with refueling aircraft, manned and unmanned spy planes and airlift assistance. Intelligence sharing about Mali has reportedly begun, but the Obama administration has yet to approve the military assistance, apparently wanting to study the situation further before getting the U.S. involved. It remains to be seen what will become of this request in light of the Algeria abduction.

It may be worth noting that the Defense Department has faced criticism for not being able to deploy special operations forces and other military assets in time to prevent the deadly September assault on the U.S. consulate in Benghazi, Libya. Africa Command had an unarmed surveillance drone over the site of the battle, but the incident ended too quickly for a mobilization. Amongst the explanations offered by the Pentagon is that Panetta, Africa Command chief Gen. Carter Ham and other senior leaders did not have sufficient time or visibility into what specifically was taking place in Benghazi to carry out a response.

Rep. Mike Rogers (R-Mich.), the chairman of the House intelligence committee, invoked Benghazi in calling for a strong reaction to the kidnapping. "The kidnapping of Americans and other westerners in Algeria brazenly raises the stakes in an already very volatile region. Militant groups and terrorists with ties to AQIM are becoming increasingly brash in their activities," Rogers said Wednesday, using the acronym for al-Qaida in the Islamic Maghreb, the terrorist group's affiliate in the region. "If we don't deal with these militant groups and terrorists swiftly and effectively, they will only pose an increasing threat in the future as they already have in Benghazi and now Algeria and Mali."

It might also be worth noting that U.S. special operations forces have extensive experience in hostage rescue.

We'll update this post as more information becomes available.