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.

A Saudi Arabian Tornado fighter crashed in the kingdom's Eastern Province during a training mission on Monday, but its crew survived, the defense ministry said.

The aircraft crashed at the King Abdul Aziz Airbase in Dhahran while on a "routine training mission," state news agency SPA quoted a ministry official as saying.

Clerics of al-Azhar on Monday elected a new mufti, or Egypt's leading interpreter of Islamic law, in an unprecedented vote signaling the Islamic institute's growing independence from the government.

Shawqi Ibrahim Abdel Karim, a professor of Islamic jurisprudence, was elected by a newly-formed council of senior clerics, which submitted its nomination for President Mohamed Morsi to ratify.

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.

Security forces on Monday arrested two daughters of opposition figure Mir Hossein Mousavi who along with his wife is under house arrest, an opposition website reported.

"Security forces raided the home of Zahra and Narges, and arrested them in the morning," Kaleme.com, which is close to Mousavi, said without citing a source.

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.

Tunisian President Moncef Marzouki's secular party said on Monday that it would stay in the coalition government, pending the resignation of key ministers from the ruling Islamist party.

"We have decided to freeze our decision to withdraw our ministers from the government, but if in one week we don't see any changes, we will quit the government," said the party chief of the Congress for the Republic, Mohamed Abbou.

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.