The Turkish government has stepped up criticism of the Syrian regime, amid increasing fears that President Bashar al-Assad is using the Kurdistan Worker's Party (PKK) as a terror tool.

Turkish Prime Minister Recep Tayyip Erdogan has launched a fresh attack against the Assad's regime, saying the army was "butchering its own people, pointing its guns at the masses".

Erdogan called for routes to be immediately opened to provide humanitarian aid in Syria, Bloomberg reported.

Turkish President Abdullah Gül had previously joined the chorus of criticism against the regime, warning it is on a "dead-end road".

"We have no trust in the Syrian government anymore," Gül said before departing for a visit to Tunisia.

"Stability and peace are no longer attainable by oppression; that era is over. Therefore, the Syrian administration should make a choice. There is only darkness and disappointment at the end of their current road," he added.

Turkey has emerged as a key regional opponent of the Assad regime, but comments from the country's foreign minister Ahmet Davutoğlu suggest that Ankara's latest warning might not only been motivated by the brutal crackdown on protesters.

The minister accused Syria of backing the PKK, which is regarded as a terrorist organisation in Turkey, and of using it as a tool to create upheaval in the country.

"Turkey is ready to discuss every option in order to protect its national security," he said, adding that Turkish security forces are monitoring a number of PKK groups entering the country from Syria and will not allow itself to be undermined.

Despite recurrent reports that the PKK has been helping the Syrian regime, the party has denied helping either Assad or his army.

"The PKK is not a tool in the hand of any country in the world to make it take up arms for it. It is a fully independent party in its decisions and its only loyalty is to the Kurdish people. It is seeking to achieve its people's national demands through its persistent struggle and, therefore, its arms are for defending its legitimate national cause and not for rent to defend repressive and despotic regimes, such as that of the Syrian one under Bashar al-Assad," the group said back in a statement in November.

"We will not defend this tyrannical bloody regime under any circumstances. We add our voice to the voices coming from all over the world in calling on the Syrian regime to stop killing the civilians, abandon the repression and violence, and open the way before the people to express their free will in a peaceful way," PKK spokesman Karawan Azardi also told the Arabic publication Asharq Al-Awsat.