Up to 70 people have been killed in an attack on a house in Hama, according to Syrian activists, BBC website reported.

It was impossible to independently verify the conflicting accounts because President Bashar Assad's regime, facing a 13-month-old uprising, has restricted access for journalists and other outside witnesses.

As the violence in Syria continues despite UN-led efforts to implement a cease-fire, the international community is becoming increasingly impatient with the Assad regime.

On Wednesday, France raised the prospect of military intervention in Syria, saying the UN should consider harsher measures if a peace plan by special envoy Kofi Annan fails.

A prominent activist urged UN observers to investigate the blast.

A pair of UN observers is stationed in Hama, part of an advance team of 15 that is to be beefed up in coming weeks to up to 300.

Amateur videos said to be of Wednesday's incident in Hama showed a large cloud of white and yellow smoke rising from a neighborhood surrounded by green fields.

In a later video, dozens of people are searching the debris, including huge chunks of cement and broken cinderblocks.

Another clip shows the bloodied body of a little girl being carried through a crowd of wailing men.

The state-run Syrian news agency SANA said rebel bomb-makers mishandling explosives set off a blast that killed at least 16 people and severely damaged at least six houses.

The Local Coordination Committees, a network of activists, said the destruction was caused by intense shelling from tanks on the areas.

''The area was shelled for a long period,'' said spokesman Omar Idlibi, denying the blast was triggered accidentally by rebels.

A second group, the Britain-based Syrian Observatory for Human Rights, said the cause of the destruction was not immediately clear.

The Observatory initially cited reports by local residents that they had come under shelling attack from regime forces.

However, the head of the group, Rami Abdul-Rahman, said he cannot be sure those reports are accurate.

Abdul-Rahman called for an investigation by UN observers.

French Foreign Minister Alain Juppe said Wednesday that France had discussed invoking Chapter 7 of the UN Charter, which can be enforced militarily, with other world powers.

US Secretary of State Hillary Clinton said last week the United Nations should move toward such a step to allow for measures like travel and financial sanctions and an arms embargo.

She didn't mention military action.

The US has for more than a year opposed the further militarization of the situation.

Any such move, however, would likely be blocked by Russia and China, which have twice used their vetoes as permanent Council members to protect Syria from condemnation and remain opposed to military intervention.

Western powers, too, don't appear interested in sending forces to another Middle East nation in turmoil.

For now, the international community remains united in support of Annan's plan, which calls for a cease-fire, to be followed by talks between the regime and the opposition on a political solution to the conflict that has killed more than 9,000 people.

That plan, however, has been troubled from the start.

Syria has failed to enact key parts of the plan, like withdrawing its forces from cities, and its troops have attacked opposition areas, killing scores of civilians since the truce was to begin on April 12. Rebel fighters, too, have attacked military checkpoints and convoys.