"We remain appalled by the loss of life, humanitarian crisis, and serious and widespread human rights abuses in Syria," a joint statement said.
"The Syrian government and all parties must immediately and fully adhere to commitments to implement the six-point plan of UN and Arab League Joint Special Envoy... Kofi Annan."
That, they said, includes "immediately ceasing all violence."
But Russia, a key ally of Syria, said there could be no regime change through force.
"One has to give an opportunity to the Syrians to sort out their affairs themselves," the Kremlin's Africa envoy, Mikhail Margelov told reporters in Washington.
"You cannot use an ax to shear your way through the Syrian crisis, you have to use a pair of pincers to somehow sort it out."
The suicide bombing was the first of its kind in Deir Ezzor, eastern Syria's biggest city, since an anti-regime uprising broke out last year, and at least 24 other people were reportedly killed elsewhere in the country.
Among the dead were a woman and her two children gunned down in the northern city of Aleppo and a 10-year-old girl killed by gunfire in the southern province of Daraa, said the Syrian Observatory for Human Rights.
A "terrorist suicide bomber" used 1,000 kilograms (2,200 pounds) of explosives in the attack on the Deir Ezzor neighbourhood of Ghazi Ayyash, said state television.
The powerful explosion left a crater 3.5 metres (yards) deep and damaged buildings within a radius of 100 metres, the channel said.
It occurred on a road housing a military and air force intelligence headquarters and a military hospital, according to the Observatory.
There was no claim of responsibility for the bombing but, as typically happens in such cases, the opposition blamed it on the regime of President Bashar al-Assad.
Elsewhere, a rocket slammed into the ruling Baath party's offices in Aleppo province, the Observatory said, a day after unprecedented anti-regime protests in the provincial capital of the same name.
"Unidentified gunmen targeted a Baath party office in Aleppo's Al-Bab town with a rocket-propelled grenade," said the Britain-based watchdog.
In Homs, sniper fire killed a civilian and blasts were heard as shells rained down on the flashpoint central city, the Observatory said, adding that four deserters and eight regime troops were among those killed Saturday.
The bombing in Deir Ezzor came a day after regime forces foiled a would-be car bombing in the same city, which is about 110 kilometres (70 miles) from the Iraqi border.
The government has repeatedly blamed bomb attacks on "armed terrorist groups" and Al-Qaeda.
G8 leaders have been meeting since Friday outside Washington, with much of their discussions focused on the bloodshed in Syria and Iran's contested nuclear programme.
Obama said on Saturday that the G8 agreed that the political process in Syria should move forward "in a more timely fashion."
"We had a discussion about Syria, we all believe that a peaceful resolution and a political transition in Syria is preferable," Obama said, flanked by leaders of the G8 industrialised nations.
What started out as a popular uprising has over time developed into an increasingly militarised revolt, after Assad's regime used force to crack down on peaceful protests.
With the killings unabated, UN-Arab League envoy Kofi Annan plans to return to Damascus soon to further efforts to find a peaceful solution to the crisis, but a date has yet to be announced.
Bahrain, Qatar and the United Arab Emirates on Saturday told their citizens to avoid travel to Syria's neighbour Lebanon, where sectarian clashes linked to the conflict have left 10 people dead.
Syria's foreign ministry, meanwhile, charged that the string of US and EU sanctions slapped on Damascus over its brutal crackdown on dissent was tantamount to "economic terrorism".
The sanctions amount to "a violation of the fundamental principles of human rights" and interference in the domestic affairs of Syria, the ministry said in a statement.
According to the Syrian Observatory, more than 12,000 people have been killed in Syria since the revolt broke out in March 2011, most of them civilians.