Turkish anti-aircraft fire shot down a Syrian warplane on Sunday as it bombed rebels fighting to seize control of a border post in northwestern Syria, in an operation described by Damascus as a “flagrant aggression.”

"Turkish air defenses targeted a Syrian fighter bomber as it struck areas of the northern province of Latakia. The plane caught fire and crashed in Syrian territory," the Syrian Observatory for Human Rights said.

Turkey's president said Sunday he believed the country would soon lift its ban on Twitter, condemned as a bid to muzzle a corruption scandal dogging the government ahead of key elections.

"I believe this problem will be over soon," Abdullah Gul told reporters in Ankara before leaving for an official visit to the Netherlands.

Syrian forces and rebels battled Sunday for a third straight day for control of a key crossing on the northern border with Turkey, the Syrian Observatory for Human Rights said.

"Fighters from (the Al-Qaida-affiliated) Al-Nusra Front and other groups have attacked the crossing and forced out regime forces and national defense auxiliaries," Observatory chief Rami Abdel Rahman said.

Turkey's government on Saturday defended its internationally condemned ban on Twitter as a "preventive measure" to stop "character assassinations" following a wave of corruption investigation leaks.

"Twitter has been used as a means to carry out systematic character assassinations by circulating illegally acquired recordings, fake and fabricated records of wiretapping," the office of Prime Minister Recep Tayyip Erdogan said in a statement sent to Agence France Presse in English.

Fighting raged Saturday between rebels and loyalist forces in Syria's northern Latakia province, a day after 34 people were killed as Islamists sought to seize a border crossing into Turkey, an NGO said.

The fighting has prompted President Bashar Assad's government to complain to the United Nations that Turkey was providing cover to rebels crossing the border from its territory.

The imprisoned Kurdish rebel leader Abdullah Ocalan used the anniversary of his party's historic ceasefire on Friday to call for a fresh start to peace talks in Turkey.

"The process of dialogue is important, although we still have not reached an agreement", said Ocalan, in a message read to 200,000 people assembled to celebrate the Kurdish new year in Diyarbakir, a city in south-eastern Turkey.

Two Albanians and a man from Kosovo have been arrested for a suspected "terror" attack that claimed the lives of two soldiers and a policeman in southern Turkey, Interior Minister Efgan Ala said Friday.

The three men were arrested after Thursday's attack, in which assailants opened fire on security forces carrying out a highway patrol near the town of Ulukisla, close to the Syrian border.

France on Friday condemned Turkey's "shocking" decision to shut down Twitter and said the aspiring EU member had to respect freedom of expression and other basic rights.

The micro-blogging site was blocked in Turkey late Thursday, just hours after Prime Minister Recep Tayyip Erdogan threatened to "wipe out" the service.

At least seven Syrian soldiers and 17 rebels were killed Friday as three Islamist groups battled to take a border crossing into Turkey.

The Syrian Observatory for Human Rights said the Islamists included the Al-Qaida affiliated Al-Nusra Front.

Turkey's combative prime minister warned on Thursday that he would eradicate Twitter in the wake of damaging allegations of corruption in his inner circle that have spread across social networks in recent weeks.

"We will wipe out Twitter. I don't care what the international community says," premier Recep Tayyip Erdogan said at an election rally in the western province of Bursa.