The assassination of former Lebanese Prime Minister Rafik Hariri seemed an unlikely catalyst for the steep increase in international scrutiny and condemnation that faced Syria in early 2005.

Yet the incident proved to be the final straw in a series of incidents over the years that raised an outcry over Damascus' links to terrorism.

American allegations of a Syrian role in the 2006 Lebanese-Israeli conflict and the Iraqi insurgency and of a Syrian connection to a February 2005 suicide bombing in Tel Aviv, also have cast the Arab republic as a supporter of terrorism and spoiler of efforts to bring peace to the Middle East.

It is a reputation that in 1979 earned Syria a spot on the U.S. State Department's inaugural list of State Sponsors of Terrorism, where it remains today.

Conflict with Israel
Syrian involvement in terrorism grew largely out of one of the more tumultuous periods of the modern history of that region -- the late 1960s and early 1970s. It was an era that witnessed the essential death of efforts to form a Pan-Arab state, and the continuing failure of Arab regimes to dominate or destroy the Jewish state of Israel.

During this time the region's major Arab armies suffered two humiliating military defeats at the hands of the Israeli Defense Forces -- in 1967 and 1973 -- and the displacement of millions of Palestinians.

For Syria, the 1967 war with Israel was particularly troublesome. It resulted in Israel's occupation of Syria's Golan Heights, a strategic parcel of land on the country's southwest border. Syria technically remains in a state of war with Israel. And given the demise of Arab unity and the depleted military powers of the Arab regimes, their leaders needed new levers of power to address the various Arab grievances, primarily those with the Israelis and their American patrons.

One way the new Syrian leader, Hafez Assad, chose to exercise what influence he had left in the Arab-Israeli arena was to support various Palestinian factions, those who advocated the creation of a Palestinian state or the destruction of Israel -- or both -- in their fight for a homeland.

In his book "Inheriting Syria: Bashar's Trial By Fire," former CIA Middle East analyst Flynt Leverett writes that Assad considered his "connections to these groups as sources of leverage and pressure for pursuing a range of strategic and tactical goals, mostly in the Arab-Israeli arena." In short, the various methods of attack these militants employed offered Assad at least the chance to try to tailor Arab-Israeli peacemaking efforts to his preferences, and to dictate the character and pace of such developments.

According to Leverett and other experts, Syria's involvement took the form of tactical and operational guidance, the safe transfer of money and weapons, the safe harbor of militants, and the training of would-be attackers in Syrian-harbored camps, among other ways. Syria also allowed groups to maintain offices in Damascus.

Alleged terrorist activity
When civil war erupted in neighboring Lebanon in 1975, Assad was offered another platform from which to attempt to influence regional events vis-à-vis Israel. Many Syrians still consider Lebanon as part of a historical Greater Syria which helped Syria justify its role in the fighting within Lebanon and helped lead to Syria's decision to deploy troops there in 1976 -- ostensibly to keep the peace.

But Syrian military and intelligence services quickly dominated the political and security apparatus of the strife-torn nation. What resulted was a situation whereby groups like Iranian-backed Hezbollah -- formed in 1982 to fight the Israeli invasion of southern Lebanon -- could use southern Lebanon as a launching pad from which to attack the Israeli military presence there, and targets inside Israel, much like Palestinian militant groups did.

By the early 1980s, Hezbollah became a major concern for the United States, too, especially after the group killed 241 Marines in Beirut in 1983, and attacked the U.S. Embassy annex there in 1984.

While Syria was not directly implicated in those attacks, Claude Salhani of United Press International wrote in the fall 2003 issue of the journal Middle East Policy, "Without Syrian support ... Hezbollah could not continue to operate its military wing for very long. The arms, munitions and support it receives from Iran pass through Syria."

While suspected Syrian terrorist activities targeted mainly Israeli and American interests in the region, Damascus did sometimes reach out to new theaters of operation. Perhaps most notorious were its two attempts -- each thwarted -- to blow up Israeli airliners in London and Madrid in 1986.

Leverett contends that those "failed operations in London and Madrid and the international reaction to them forced the Assad regime to change the nature of its support" for terrorist organizations, focusing on more indirect means of aid. A 2003 State Department report "Patterns of Global Terrorism" said that the Syrian government "has not been implicated directly in an act of terrorism since 1986."

Terrorism or resistance
Despite widespread accusations, debate continues over the level at which Syria supports terrorist activities.

In 2006, Israel accused the Syrian regime of helping Iran arm and finance Hezbollah fighters as they battled Israeli troops in the 34-day conflict.

The regime itself consistently denies involvement in terrorist activities, characterizing Palestinian violence against certain Israeli targets as legitimate resistance to the Israeli occupation.

Syrian-American scholar Murhaf Jouejati argued before the Senate Foreign Relations Committee in October of 2003 that while "Syria indeed hosts a number of militant Palestinian organizations ... there is no evidence to support the claim that Syria provides material or financial assistance to these groups." But Jouejati agreed that "the hypothesis according to which Syria allows them to engage in business and other money-making activities to finance and sustain their operations is plausible."

Still, Syria remains largely isolated for several reasons. The State Department has kept the country on its infamous list, and argues Syria continues to operate through proxies such as Hezbollah and the Palestinian militant group Hamas.

Syria is the only major Arab state not to have reached some form of peace deal with Israel as Egypt and Jordan have done. Such developments have left Syria with fewer methods by which to influence regional events, but it has been accused of continuing to use those that do remain.

The United States accuses Syria of continuing to harbor ex-Iraqi Baathists thought to be directing and funding the insurgency with Iraqi money hidden in Syria.

And despite Syria's efforts to influence regional politics, the main sources, experts say, driving Syrian involvement in terrorism -- the Arab-Israeli stalemate and the presence of Israeli troops in the Golan Heights -- remain. With no sign either issue can be resolved any time soon, it remains unclear as to whether Syria will maintain its current policies or choose to abandon the tactics that have left it isolated internationally and regionally.

-- Compiled by David Butterworth for the Online NewsHour