William Hague has called for a UN security council resolution warning Syria of "serious consequences" for breaches of the peace plan, as the UN envoy Kofi Annan arrived in Moscow to urge stronger Russian support for pressure on Damascus.
"The situation in Syria continues to deteriorate alarmingly. We have seen even more terrible massacres in recent days," the foreign secretary said during a visit to Libya.
"The British government believes it is it is imperative to have a chapter seven resolution of the security council, which should mandate the implementation of the Kofi Annan peace plan and of a transitional government."
He said the language of the resolution should "threaten serious consequences for non-compliance in that plan", but did not spell out what those consequences should be.
Hague's comments buttress calls by the UK and US governments for a firmer line on Damascus, but Russia has yet to signal it would support such a resolution at the UN.
There were reports of renewed fighting around Damascus. On Sunday, the International Committee of the Red Cross declared that Syria was in a state of civil war.
The mandate of the UN observer mission to Syria expires on Friday and there is still no agreement among key members of the security council about the nature of any new mandate.
Hague also revealed that Metropolitan police officers would visit Tripoli this week to continue investigating the killing of PC Yvonne Fletcher outside the Libyan embassy in London in 1984. "I can see very clearly that this is being pursued with great energy in the UK and Libya," he said.
Hague dismissed suggestions of foot-dragging by either London or Tripoli, after press reports from Libya at the weekend alleged a lack of action on the case. He said Libya's prime minister, Abdurahim el-Keib, told him he "was surprised to hear comments to the contrary and apologised for any accounts that came from his own department to the contrary".
The fall of Muammar Gaddafi last year raised hopes that a new government in Tripoli would open the door for British police to travel to Libya to investigate the case. In December, the Foreign Office minister Alistair Burt met Libyan officials in Tripoli and announced that the new government had agreed to co-operate.
In March, Libya's interior minister, Fawsi Abdulal, said there was no legal mechanism in place to allow a UK police visit, and predicted that no such visit could happen before the general election, which was held this month. In May, Keib visited London to announce that co-operation would be offered after all, and in June, Met officers made their first visit to Tripoli to work on the case.
