The Syrian president has repeated criticism that the UN inquiry into the killing of former Lebanese PM Rafik Hariri is biased against Syria.
Mr Assad defended Syrian sovereignty
In a speech in Damascus, Bashar al-Assad said the investigators had reached their conclusions first, and looked for the evidence afterwards.
He hinted he would refuse a request to give evidence in person in the case.
The commission has implicated Syrian officials in the killing last February, but Damascus denies any involvement.
The state has faced international pressure since the attack, when Syrian forces were still stationed in Lebanon.
The assassination led to widespread protests in the country and forced Syria to end its 29-year-old military presence there last April.
Last month, the UN Security Council passed a resolution endorsing a six-month extension of the inquiry and renewing its call for Syria's full co-operation.
But President Assad told an audience of Arab lawyers that the UN panel "was a condemnation committee, not an investigation committee".
He pledged to co-operate, but said that Syrian sovereignty must be respected.
"When we say the investigation is based on national sovereignty that means we have set a limit," Mr Assad said.
Instead, he supported a call for a commission to investigate what he described as the assassination of Palestinian leader Yasser Arafat, who died in a French hospital just over a year ago.
The speech was regularly interrupted with angry chants of support, but the Syrian leader was strangely downbeat, the BBC's Jon Leyne reports from Damascus.
Mr Assad said Syria and the Arab world were being targeted by what he called outside forces who wanted to control their resources.
Grip on power
In his speech, Mr Assad also revealed that he had decided to carry out political reform.
He said he was studying projects to free up the party system and draw more Syrians into the political process, adding that the government was working towards making the judiciary independent.
But reforms had to be "consistent with domestic requirements, and we refuse to accept them being imposed from abroad", he said.
At the moment the Islamist movement, the Muslim Brotherhood, is banned in Syria, and there are estimated to be up to 1,500 political prisoners.
However, Mr Assad's address follows the early release of five leading political prisoners earlier this week, after 45 months of their five-year prison sentences.
The human rights group Amnesty International has also been allowed into the country for the first time since 1997.
But our correspondent says there is still no sign of the major changes that seemed possible when President Assad took office in the year 2000.
There has been no sign that the members of the ruling circle are willing to give away much of their power.