BAGHDAD - It was a brazen, complex attack worthy of Iraq's al-Qaida at its peak. Two bombs minutes apart killed, maimed and distracted while a team of suicide attackers blasted into a Baghdad police base to try to free jailed insurgents.
Tuesday's high-profile assault on a anti-terrorism police unit in Baghdad was the latest in a drive by the Islamic State of Iraq, al-Qaida local affiliate, to make good on a pledge to win back ground lost in its war with American troops - its leader has even threatened to strike at the United States.
Insurgents ultimately failed to free their prisoners, but the intended message was clear: we're back.
With Sunni Muslim militants trickling into neighboring Syria to battle Syrian President Bashar Assad, security experts say al-Qaida is reaping funds, recruits and better morale on both sides of the border, reinvigorating it after years of losses against US forces and their Iraqi allies.
Islamic State of Iraq and other Sunni militant groups hate Assad's minority Alawite sect, a distant offshoot of Shi'ite Islam, which they see as a heretical oppressor of Sunnis.
Hostile to Shi'ites in general, they also oppose the Shi'ite-led government of Iraqi Prime Minister Nuri al-Maliki. Iran, the major Shi'ite power in the region, is a firm ally of Assad and wields great influence in Baghdad.
Al-Qaida appears to be exploiting Sunni-Shi'ite tensions fueled by the increasingly sectarian conflict in Syria. Many Sunnis in Iraq are already disgruntled with what they see as Maliki's determination to minimize their share in power.
"The Syrian crisis is a venue in which an Iraqi-dominated al-Qaida branch is better able to attract fighters and resources to its cause," said Ramzi Mardini, an analyst with the Institute for the Study of War in Washington. "This may be a revival of confidence on the part of Sunni extremists."Changing sides
Once at the heart of a Sunni insurgency against US-led forces, al-Qaida lost many commanders to Iraqi and US troops. Sunni tribes turned the tide against it from 2007, when they fought the group with US-supplied guns, partly in revulsion at the indiscriminate carnage it had inflicted on civilians.
Iraq's violence has eased since the sectarian bloodbath of 2006-2007, but each month since the last American troops left in December al-Qaida has claimed responsibility for at least one major, well-coordinated attack.
A return to all-out sectarian violence looks unlikely, but the possible fall of Syria's Assad worries Iraqi Shi'ite leaders who fear that a hardline Sunni government could come to power instead, emboldening Sunni militants in Iraq.
Already, Baghdad says that seasoned al-Qaida fighters are crossing the 680 km border into Syria to liaise and conduct attacks on Assad's government. That hands Islamic State of Iraq new legitimacy in the eyes of some Sunnis, experts say.
Along Iraq's western frontier with Syria, near Albu Kamal, unrest across the border has fired up sympathies in a Sunni heartland with shared tribal and family ties.
Al-Qaida influence is strong in some remote border villages, and Iraqi forces skirmish daily with smugglers and insurgents sending fighters and weapons into Syria, said one senior Iraqi security official.
"The religious legitimacy of the Syria war and the increase of funding and fighters almost unquestionably benefits Al Qaeda in Iraq," said Seth Jones, a counter-terrorism expert at Washington's RAND Corporation and an author on al-Qaida. "It is heavily involved in overseeing the war in Syria."New chapter, new tactics
America's withdrawal took with it US intelligence gathering capabilities, handing insurgents more operational space in former strongholds such as Anbar province and areas where local political infighting hobbles Iraqi armed forces.
At the start of the Muslim holy month of Ramadan at the end of July, a rare communique from al-Qaida's local chieftain, Abu Bakr al-Baghdadi, announced a renewed jihad to recapture areas lost during the years of conflict with American forces.
In a fiery message about his muhahideen combatants, Baghdadi also warned Americans: "You will soon see them in your homes. The war has only just started."
Even before his call to arms, June witnessed some of the severest attacks attributed to al-Qaida in Iraq since the US pullout, including a surge in bombings on Shi'ite pilgrims and a suicide attack on a Shi'ite religious office in Baghdad.
July was Iraq's bloodiest month in the past two years with 325 people killed in attacks, most of them civilians.
Though al-Qaida's support had dwindled in Iraq because of civilian casualties, its bombings now focus on Shi'ite targets, government offices and local security forces as it seeks to inflame sectarian tensions and undermine Maliki.
The group, once a magnet for foreign fighters who often antagonized locals, has now reverted to a core of Iraqis hardened by the anti-American insurgency and in US jails.
"These organizations have shown a resilience by adapting and forming small diffuse cells," said John Drake, at AKE Group consultancy. Al-Qaida in Iraq is now "seen as a much more domestic organization, so it could actually have more support among some members of the Iraqi public," he added.