Syria's top Christian leader said on Tuesday at the funeral for victims of a deadly church bombing that President Ahmed al-Sharaa's government bore responsibility for not protecting minorities and his condolences were insufficient.

At least 25 worshippers died on Sunday when a suicide bomber blew himself up at the Mar Elias Church in Damascus, the first such attack since Sharaa's Islamist-led government seized power in December after the Assad family dynasty's toppling.

The attack, which the government blamed on the Islamic State militant group, reinforced doubts among minorities about whether they can rely on government assurances of protection.

"With love and with all due respect, Mr. President, you spoke yesterday by phone... to express your condolences. That is not enough for us," the Greek Orthodox Patriarch of Antioch, John (X) Yazigi, said at the funeral, drawing applause.

"We are grateful for the phone call. But the crime that took place is a little bigger than that."

The US State Department condemned what its spokesperson Tammy Bruce described as "a brutal and cowardly attack" and called on the Syrian government to hold all perpetrators of violence accountable and ensure the security of all Syrians, including members of religious and ethnic minorities.

She said Washington continued to support the Syrian government "as it fights against forces seeking to create instability and fear in their country and in the broader region."

Christians made up around 10% of Syria's pre-war population of 22 million, but their numbers shrunk significantly during the 14-year conflict, mainly through emigration. Only a few hundred thousand are now estimated to be living in Syria.

Yazigi said the government must prioritize protection for all. "What is important to me - and I will say it - is that the government bears responsibility in full," Yazigi said of the church attack.

Hundreds were at the service in the nearby Church of the Holy Cross to bury nine of the victims, whose bodies were placed in simple white coffins adorned with white flowers.

Social affairs minister Hind Kabawat - the only Christian and only woman in Syria's new government - attended.

On Monday, Sharaa said the attack was a crime hurting all Syrians but did not use the word "Christians" or "church".

The government said security forces raided hideouts used by Islamic State, killing two of its members including one who facilitated the suicide bomber's entry into Mar Elias Church.

IS did not issue a statement of responsibility.