BAGHDAD — Al-Qaida is rebuilding in Iraq and has set up training camps for insurgents in the nation’s western deserts as the group seizes on regional instability and government security failures to regain strength, officials say.

Iraq has seen a jump in al-Qaida attacks over the past 10 weeks, and officials believe most of the fighters are former prisoners who have either escaped from jail or were released by Iraqi authorities for lack of evidence after the U.S. military withdrawal last December.

Many are said to be Saudi or from Sunni-dominated Gulf states.

During the war and its aftermath, U.S. forces, joined by allied Sunni groups and later by Iraqi counterterror forces, managed to beat back al-Qaida’s Iraqi branch.

But now, Iraqi and U.S. officials say, the insurgent group has more than doubled in numbers from a year ago — from about 1,000 to 2,500 fighters. And it is carrying out an average of 140 attacks each week across Iraq, up from 75 attacks each week earlier this year, according to Pentagon data.

“AQI is coming back,” Sen. Lindsey Graham, R-S.C., said last month while visiting Baghdad.

The new growth of al-Qaida in Iraq, also known as the Islamic State of Iraq, is not entirely unexpected. Last November, the top U.S. military official in Iraq, Army Gen. Lloyd Austin, predicted “turbulence” ahead for Iraq’s security forces.

But he doubted Iraq would return to the days of widespread fighting between Shiite militias and Sunni insurgents, including al-Qaida, that brought the Islamic country to the brink of civil war.

While there’s no sign of Iraq headed back toward sectarian warfare — mostly because Shiite militias are not retaliating to their deadly attacks — al-Qaida’s revival is terrifying to ordinary Iraqis.

Generally, the group does not does not launch attacks or otherwise operate beyond Iraq’s borders. For years, it has targeted Shiite pilgrims, security forces, officials in the Shiite-led government and — until it left — the U.S. military. Tuesday, a series of bombings and drive-by shootings killed six people, including three soldiers and a judge, in Baghdad and the former al-Qaida strongholds of Mosul and Tal Afar in northern Iraq.

Each round of bombings and shootings the terror group unleashes across the country, sometimes killing dozens on a single day, fuels simmering public resentment toward the government, which has unable to curb the violence.

And the rise of Sunni extremists who aim to overthrow a Shiite-linked government in neighboring Syria has brought a new level of anxiety to Iraqis who fear the same thing could happen in Baghdad.

“Nobody here believes the government’s claims that al-Qaida is weak and living its last days in Iraq,” said Fuad Ali, 41, a Shiite who works for the government.

“Al-Qaida is much stronger than what the Iraqi officials are imagining,” Ali said. “The terrorist group is able to launch big attacks and free its members from Iraqi prisons, and this indicates that al-Qaida is stronger than our security forces. The government has failed to stop the increasing number of victims who were killed since the start of this year.”

In the vast desert of western Iraq near the Syrian border, security forces have discovered the remnants of recent insurgent training camps, said Lt. Gen. Ali Ghaidan, commander of the army’s ground forces. An army raid last month on Iraq’s sprawling al-Jazeera region, which spans three provinces, found a 10-tent campsite littered with thousands of bullet shell casings, Ghaidan told The Associated Press.