Syrian President Bashar al-Assad wavered between concession and defiance in his first public address in over two months, saying for the first time that some protesters had legitimate demands, but repeating his justification for a military crackdown.

The Syrian president continued to blame recent unrest on what he said were armed groups seeking to destroy Syria, and on a foreign plot. "We have to isolate the saboteurs," he said.

Syria's President Bashar al-Assad gave a speech at Damascus University in Damascus, Syria. Associated Press

Mass demonstrations continue in Syria after Assad's pledged reforms have yet to yield change. Video courtesy of Reuters.

Mr. Assad said his government would continue to review the possibility of reforms to Syria's constitution—which gives his ruling Baath party a monopoly on political power—and of changes to laws governing parliamentary elections and the media. He suggested the constitution could be redrafted entirely if a national dialogue produced a consensus. The speech was otherwise short on specifics and he didn't announce new reforms.

The speech failed to win over domestic and foreign critics and sparked further protests across the country. The Local Coordinating Committees, a network of Syrian activists leading the organization of protests, slammed the speech as a repetition of "unfulfilled promises, veiled or direct threats and false accusations."

Activists described the speech as defiant, after a prolonged silence from Mr. Assad and rising international pressure on his regime. The president hadn't spoken publicly since April 16.

"If he gave this speech three months ago, things may have been different," said Molham al-Drobi, a member of Syria's exiled Muslim Brotherhood who was voted by a group of activists onto an executive committee last month.

After the speech, the Obama administration repeated its call for an end to violence against protesters and a beginning to meaningful political dialogue. "What's required in Syria is action, not words, not promises," said White House Press Secretary Jay Carney.

In Turkey, with which Mr. Assad's relationship has soured amid the crackdown, President Abdullah Gul said Mr. Assad should say he would make a transition to a multiparty system, and that "everything will be organized according to the wishes of the Syrian people," Turkey's state-run news agency Anadolu Ajansi reported. "Once he has said this, everything that is happening can be prevented and brought under control," Mr. Gul said.

Angry Syrian refugees protest over President Bashar al-Assad's promises of creating a national dialogue. Video courtesy of Reuters and photo courtesy of AP.

The protests, which have erupted in all of Syria's major cities but remain contained in the capital, have posed the greatest challenge to the 11-year rule of Mr. Assad, who inherited power from his father. Syria's government has sent the military to stamp out dissent in several cities in the country of 21 million. An estimated 1,400 people have been killed in the unrest, with thousands more missing or detained.

As Mr. Assad spoke to an audience at Damascus University in the Syrian capital, thousands of Syrian refugees on both sides of the northern border with Turkey began to chant: "The people want the downfall of the regime."

In the mountainous region near the Turkish border, activists-in-hiding said they trekked to a village to watch the speech broadcast on state television.

Activists in Damascus said security forces locked down two suburbs with checkpoints after protesters marched to denounce the speech. Protests and responses by security forces were also reported in Aleppo and Latakia, according to Avaaz, a global activist network.

In Aleppo, Syria's second-largest city, hundreds of students marched against the regime, according to Avaaz. More than 1,000 riot police raided student dorms and detained over 50 students, Avaaz said. In the coastal city of Latakia, security forces shut down the main streets after the speech ended, chasing and attacking protesters in side streets, Avaaz said.

Wearing a black suit and dark gray tie, Mr. Assad appeared tense, stumbling over his words and straying from his notes several times in the hour-long speech, in contrast to two previous public addresses made since the start of protests in mid-March. He began by dismissing "rumors" related to his absence in public, saying the delay was due to extensive meetings and consultations with local delegations, including the youth, who he said had affirmed their love and support for him.

Mr. Assad offered condolences to the families of those killed in the past three months, paid tribute to the army, and said he would focus on strengthening "internal weak points" and protecting Syria's unity.

The unrest has started to test Syria's religious and ethnic fabric, an arrangement in which Mr. Assad—of the minority Alawite sect—rules over a Sunni majority in a secular government.

Suggesting Syria's unrest was distinct from other uprisings in the Mideast, he said the region's youth could learn from Syria's.

He also conceded that among people marching on Syria's streets were citizens with demands which the government sought to fulfill. He stressed the need to differentiate between those people and "saboteurs."

Mr. Assad appealed for help to restore confidence in the country's economy and called on Syrians fleeing to Turkey to return to their homes and restore normalcy to daily life.

Mr. Assad announced the end a decades-old state of emergency in March, and since then, his government has announced the formation of several committees to study electoral, constitutional, and media sector reform. On Monday, he said the committees had made progress.

Mr. Assad said a process of national dialogue announced last month could lead to a change to the article of the country's constitution that gives the Baath party ultimate power. He didn't specify how or when that might happen. Such a change has been at the center of opposition demands and is seen as key to paving the way to a multiparty democracy. Syria has been under Baath rule since 1963, with Mr. Assad, 45 years old, at the helm since taking over from his father 11 years ago.

—Marc Champion

and Ayla Albayrak in Istanbul contributed to this article.

Corrections & Amplifications

Syria and Turkey have had close relations since 2002, after a period of tension preceding that in the 1990s. An earlier version of this article misstated that Syria and Turkey have been longtime allies.

Write to Nour Malas at nour.malas@dowjones.com