U.S. officials allege Iranian intelligence is actively helping al-Qaida fighters in Syria, even though the jihadists are battling to bring down Syrian President Bashar Assad, Tehran's key Arab ally.

At first glance, this would seem to fly in the face of a high-profile effort by U.S. President Barack Obama to achieve detente with Iran, America's longtime adversary, which -- if it comes off -- would dramatically alter the geopolitical landscape of the Middle East.

At a deeper level, analysts say it makes sense, inasmuch as Tehran helping al-Qaida reinforce jihadist fighters engaged in vicious infighting with other Syrian rebel forces, including Islamists, means the divided insurgents are weakening themselves and not Assad's beleaguered regime in Damascus.

The U.S. Treasury Department, targeting a diverse group of entities and individuals for allegedly evading international sanctions against Iran, aiding missile proliferation and supporting terrorism, said last week Iran's Ministry of Intelligence and Security, or MOIS, was working with al-Qaida operatives directing jihadists to Syria.

Treasury has made this claim before. In February 2012, it cited the MOIS, Iran's principal intelligence service, for supporting terrorist groups, "including al-Qaida and al-Qaida in Iraq ... again exposing the extent of Iran's sponsorship of terrorism as a matter of Iranian state policy."

A year earlier, it singled out a senior al-Qaida operative it identified as a Syrian named Ezedin Abdel Aziz Khalil, aka Yasin al-Suri, as the group's chief facilitator in Iran.

He allegedly is still operating there. Al-Jazeera reported in January al-Suri "is more active than ever."

Analyst Thomas Joscelyn of the Long War Journal, which tracks global terrorism, says: "Al-Suri operates under an agreement that was struck between the Iranian regime and al-Qaida years ago. He first began operating inside Iran in 2005.

"It's not clear why the Iranian government would allow al-Suri to act as a facilitator for al-Qaida's operations in Syria. ... The Iranian regime, however, has mastered duplicity and may have unknown reasons for keeping tabs on al-Qaida's operations."

With U.N.-sponsored Syrian peace talks under way, there are indications the United States and other Western powers are prepared to allow Assad to stay on as Syria's leader, possibly of a truncated state, if that helps avoid allowing the increasingly sectarian civil war to ignite a region-wide conflict between Islam's mainstream Sunni sect and the rival Shiite sect.

At the same time, Obama is making some progress in persuading the new centrist government in Tehran to bury the hatchet on 35 years of confrontation that began when Ayatollah Ruhollah Khomeini toppled the U.S.-backed shah of Iran in January 1979.

It's not clear why the U.S. Treasury Department would want to rock the boat now by accusing Iran's intelligence service of aiding al-Qaida, and presumably jeopardizing Obama's grand design.

On the face it, the Americans appear to be saying what's happening is a byzantine plot that brings together two groups in the Middle East who are polar opposites and who've been engaged in a religious and ideological conflict for years.

Analysts say such Machiavellian machinations, drawing together what seem to be incompatible elements to achieve an objective that benefits both, are not unusual in the Middle East.

But this one seems to be particularly important because of the geostrategic consequences that could ensue at a time of critical and possibly epochal change in the Middle East.

The Sunnis are the dominant sect in Islam. The Shiites broke away from orthodox Islam in a dynastic feud over who should succeed the Prophet Muhammad after his death in 632. The Sunnis won.

These days, the two sects are increasingly at odds in a religious-ideological conflict, principally involving Iran and Sunni-dominated Saudi Arabia, a dispute that is intensifying alarmingly, not just in Syria, but in Iraq, Lebanon and Pakistan.

There's long been confusion about whether Tehran's intelligence chiefs maintained links with al-Qaida to manipulate it into carrying out operations that ultimately benefit the Islamic republic.

One appears to be letting al-Qaida smuggle fighters to Syria, where the two main jihadist groups -- the Islamic State of Iraq and the Levant and the al-Nusra Front -- are waging a ferocious internecine war that benefits the Iranian-backed Assad regime while weakening al-Qaida.

Syria's opposition National Coalition accused ISIL Feb. 5 of being tied to the Damascus regime and "directly or indirectly" serving its interests by dividing the rebel forces.