In a powerful address at a conference of the Arab lawyers union in Damascus on Saturday, al-Assad said: "What is happening between Syria and Lebanon is part of a global plot against all Arabs, which has many facets."
The Syrian president said he was in favour of the UN commission of inquiry into the murder of former Lebanese prime minister Rafiq al-Hariri continuing its work, but on a legal and not political basis.
"Total cooperation with the UN commission must be made while respecting principles of national sovereignty, the neutrality of the inquiry and on a legal basis," he said. "National sovereignty is the strongest thing and not UN resolutions."
Syria has come under sustained international pressure for internal reform following the 14 February assassination of al-Hariri, which was widely blamed on Damascus.
Al-Assad has denied responsibility for the killing and a string of other political assassinations in Lebanon over the past year.
Al-Assad said the UN inquiry was determined to blame Syria regardless of the facts but vowed it would not bow to international pressure.
He said Damascus was still willing to cooperate with UN investigators but not at the expense of its national sovereignty.
"They have created a condemnation committee, not an investigation committee," al-Assad told the conference, convened in Damascus under the headline Defending Syria.
"Of the many assassinations that Israel carried out in a methodical and organised way, the most dangerous thing that Israel did was the assassination of President Yasser Arafat"
"They identified a perpetrator even before any accusation was made and from there they identified a single suspect, Syria, instead of several suspects, and then began searching for evidence to condemn Syria."
A Security Council resolution passed in October demanded Syria cooperate with the investigation or face unspecified further action.
Al-Assad vowed in his speech to speed up reforms aimed at introducing more political freedom and a measure of democracy to Syria but said he would resist foreign pressure for change.
"Reform begins with our domestic needs and we totally reject any reform imposed from outside under any slogan or pretext," he told the gathering of Arab lawyers.
Syria has repeatedly denied any
involvement in al-Hariri killing
"We are still at the beginning of a long road, but we will not let it be said that we have achieved nothing. Maybe the [pace] is slow ... but we are speeding as much as possible."
Syria freed from jail this week five opposition figures whose release had been demanded by several Syrian and Arab parties.
They had been detained since 2001 for violating the constitution after calling for reform during what the Western press has dubbed the "Damascus Spring".
Syria's ruling Baath party agreed in June to draft a new law that would allow independent political parties and overhaul election laws. It also partially lifted an emergency law in place since the Baath seized power in 1963, but activists have
called for it be abolished entirely.
"We are undertaking several projects that will boost public participation and help enrich democratic life, whether it be linked to the parties law or to election and local government laws," al-Assad said.
"We are also working on strengthening institutions, the rule of law and judicial independence to activate political life, enrich our national activities and remedy some negative symptoms it is facing."
Al-Assad accused Israel of assassinating former Palestinian leader Yasser Arafat, the cause of whose death 14 months ago remains a mystery.
"Of the many assassinations that Israel carried out in a methodical and organised way, the most dangerous thing that Israel did was the assassination of President Yasser Arafat," al-Assad told the gathering of Arab lawyers.
"This was under the world's gaze and its silence, and not one state dared to issue a statement or stance towards this, as though nothing happened."
Arafat died in Paris on 11 November 2004 at the age of 75 after being rushed from his West Bank compound to a French military hospital.
Israel has denied being responsible for the deterioration in Arafat's health before his death and has denied poisoning him.
Israeli officials said he had access to medical treatment, food, water and medication during the two years he spent in his battered compound in Ram Allah, which was besieged by Israeli troops for months in 2002.
French doctors denied rumours that Arafat was poisoned but have refused to publish his medical reports, citing strict privacy laws.
Arafat aides had quoted doctors as saying he had a low count of platelets, which help the blood to clot. They later said he had gone into a coma, suffered a brain haemorrhage and lost the use of his vital organs one by one. But no definitive cause of death was announced.