Syrian rebels once welcomed fighters of the jihadist al-Nusra Front with open arms but disputes over the extremists' strict interpretation of Islam are beginning to strain the ties.

In a rebel rear base at Atme in northern Syria, on the border with Turkey, at least four fights have broken out in recent weeks between jihadists and mainstream rebels, witnesses and residents told Agence France Presse.

Syrian President Bashar Assad on Monday stressed that his regime, battered by nearly two years of revolt, will not submit to pressure or "plots" against it, reported state news agency SANA.

"Syria will remain the beating heart of the Arab world and will not give up its principles despite the intensifying pressure and diversifying plots not only targeting Syria, but all Arabs," Assad said at a meeting with a Jordanian delegation in Damascus.

At least 13 people were killed and dozens wounded when a Syrian mini-bus exploded Monday near the border between Turkey and Syria, officials said, though the cause was not immediately clear.

"All possibilities are on the table, including political motives," Deputy Prime Minister Bulent Arinc said after unidentified explosives triggered the "powerful blast".

Jihadist rebels killed 14 Syrian intelligence officers in twin suicide car bomb attacks against their offices in the northeast province of Hasakeh on Monday, the Syrian Observatory for Human Rights said.

"At least 14 members of state security and military intelligence were killed when Al-Nusra Front fighters detonated car bombs in front of the state security headquarters and a military intelligence building in the town of Shadada," the watchdog said, citing sources on the ground.

Progressive Socialist Party leader MP Walid Jumblat accused some “outsiders” of seeking to tarnish Arsal's image, demanding that all sides support the army and refrain from victimizing the Bekaa town.

He said in his weekly editorial in the PSP-affiliated al-Anbaa website: “Some small MPs and sons of MPs are exploiting the confusion within the Mustaqbal Movement in order to achieve governmental gain.”

The head of Syria's opposition coalition, Ahmed Moaz al-Khatib, said Monday he had received "no clear response" from the regime of President Bashar Assad over his offer of dialogue.

Khatib said in late January he was prepared to hold direct talks with regime representatives who did not have "blood on their hands," and so long as the discussions addressed replacing Assad.

Rebels on Monday seized control of the largest dam in Syria, a vital barrier along the Euphrates River in the northern province of Raqa, the Syrian Observatory for Human Rights said.

"The rebels took control of the dam, which is still in operation. They are guarding both entrances but have forbidden the fighters from staying inside for fear the regime will bomb it," Observatory director Rami Abdel Rahman told Agence France Presse.

Maronite Patriarch Beshara al-Rahi will head to Iraq and Russia soon after he made a short visit to Syria over the weekend.

According to An Nahar newspaper published on Monday, al-Rahi will head to Iraq during the upcoming two weeks to attend the enthronement of Louis Sako, the new patriarch of the Chaldean church.

Bassam al-Dada, an adviser to the commander of the rebel Free Syrian Army, has denied reports that the kidnapper of Lebanese pilgrims in Syria was killed.

Al-Liwaa daily on Monday quoted al-Dada as saying that Amar al-Dadikhi of the rebel North Storm brigade, also known as Abu Ibrahim, who last May kidnapped 11 Lebanese pilgrims on their way home from Iran, was being held in Turkey.

U.N.-Arab League peace envoy Lakhdar Brahimi met Sunday in Cairo with Syrian opposition leader Ahmed Moaz al-Khatib and urged him to keep seeking dialog with the Damascus government, the U.N. said.

Brahimi met with Khatib and the vice president of the National Coalition, Riad Seif.