BAGHDAD -- The wounded Syrian government troops were returning to their country in trucks escorted by Iraqi soldiers. They had almost reached the border, near the frontier town of Akashat, when the attackers struck.
Regional intelligence officials saw the March 4 ambush, which left 48 dead, as evidence of a growing, cross-border alliance between two powerful Islamic extremist groups -- al-Qaida in Iraq and Jabhat al-Nusra, or Nusra Front, in Syria. Nusra Front is the most effective rebel faction fighting President Bashar Assad's regime, and the United States has designated both Sunni jihadi groups as terrorist groups.
Iraqi intelligence officials say the burgeoning cooperation is pumping new life into the Sunni insurgency in their country. They point to nearly 20 car bombings and suicide attacks that killed more than 65 people, mostly in Baghdad, on the eve of last month's 10th anniversary of the U.S.-led invasion of Iraq.
The alliance is also nurturing Nusra Front, which emerged as an offshoot of Iraq's al-Qaida branch in mid-2012 to battle Mr. Assad's regime as one of a patchwork of disparate rebel groups in Syria. Nusra Front's presence on the battlefield complicates desperately needed international support for Syrian rebels because foreign backers do not want to bolster Islamic extremist groups.
Two Iraqi intelligence officials said the cooperation reflected in the attack on the wounded Syrian troops prompted the Baghdad government to request U.S. drone strikes against the fighters. They spoke on condition of anonymity because they were not authorized to discuss the subject.
A U.S. official confirmed that elements within Iraq's government had inquired about drone strikes. But the official said the United States was waiting to respond until the Iraqi leadership's top level makes a formal request, which hasn't happened.
Iraq is also turning elsewhere for assistance. Staff Lt. Gen. Mohammed al-Askari, a Ministry of Defense spokesman, said that in Iraq's last weapons deal with Russia, Baghdad requested aircraft and heavy weapons to try to seize control of the Iraq-Syria border region where the groups are operating.
The two Iraqi intelligence officials said the jihadi groups are sharing three military training compounds, logistics, intelligence and weapons as they grow in strength around the Syria-Iraq border, particularly in a sprawling region called al-Jazeera, which they are trying to turn into a border sanctuary that both groups can exploit. It could serve as a base of operations to strike either side of the border.
"We are very concerned about the security situation in Iraq," said Iraqi government spokesman Ali al-Moussawi. He said Iraqi ground troops and the country's tiny air force were unable to quell the militant activity in the border zone. "This area is a nest of terrorist cells," he said.
A Jordanian counterterrorism official said al-Qaida in Iraq was assisting Nusra Front "with all possible means, including weapons, fighters and training."
Another regional security analyst cited the attack on the wounded Syrian troops in Iraq as decisive proof of cooperation. "This is operational collaboration," the analyst said, requesting anonymity because of the subject's sensitivity. "The transfer of weapons, tactics and ideas, what they call complex suicide attacks."
Iraq and Syria's other neighbors -- Jordan, Lebanon, Turkey and Israel -- all fear the spillover effects of the 2-year-old civil war. Iraq, Lebanon and Syria all share a similar, fragile ethnic mix, and the concern is that the conflict could cause sectarian warfare between Sunnis and Shiites to spread throughout the region.
Under Iraqi Prime Minister Nouri al-Maliki's Shiite-led government, already-tense relations with minority Sunnis have worsened. There are also long-standing strains between Arabs and Kurds, who control an autonomous region in Iraq's north.
In Syria, Mr. Assad is a member of the Alawite sect, an offshoot of Shiite Islam, and his security forces are heavily stocked by fellow Alawites and Shiites. But Alawites are a minority, and the opposition fighting him is predominantly made up of majority Sunnis.