Seoul: Syrian President Bashar al-Assad has thanked North Korean leader Kim Jong-Un for supporting his "just cause" as his forces battle an uprising against his regime, Pyongyang state media said Thursday.

In a message congratulating the leader on his recent appointment to the position of "Marshal", Assad expressed gratitude to Kim for backing his regime amid deepening international isolation, the North's official news agency said.

"I would like to express my deep thanks to your excellency," it said.

Assad thanked "the leadership of (the North) and the friendly Korean people for having rendered support and encouragement to our just cause against the moves of the world powers to interfere in our internal affairs".

The note, which state media said was received by the new leader on Tuesday, gave no details about what the support consisted of.

Assad's bloody crackdown on the uprising against his rule, which has escalated into full-blown conflict between rebels and regime forces, has drawn global condemnation.

But world powers have failed to take effective action to stop the increasingly bloody fighting, with three attempts to get resolutions on Syria through the UN Security Council vetoed by Russia and China.

A peace plan by UN-Arab League envoy Kofi Annan has also so far failed to stop the violence, that has left thousands dead.

In Syria Thursday, troops prepared to launch an all-out offensive on rebel-held districts across Aleppo, a security source said, as pro-regime media warned of a looming "mother of all battles".

Kim was made "Marshal" of North Korea last week, a title previously held by his late father, in the latest of a series of moves analysts say are aimed at strengthening his control over the country's powerful military.