Two Iranian warships sent by Tehran to the Mediterranean last week to help "train the Syrian navy" entered the Suez canal early on Tuesday on their way back to Iran, a canal authorities source told Agence France Presse.

The ships, a destroyer and supply vessel, came from the Syrian port of Tartus and were heading south towards the Red Sea, the source said, adding that they were due to complete their transit of the canal by Tuesday afternoon.

Syrian forces killed 57 civilians Tuesday as they blitzed the city of Homs and a village in Idlib province, monitors said, as the Red Cross sought a truce to deliver aid and the United Nations demanded unimpeded access for aid groups.

The escalation comes as Russia, a key ally of President Bashar al-Assad's regime, said it will boycott an international conference in Tunis this week aimed at seeking political change in Syria and China refused to commit.

Foreign Minister Adnan Mansour confirmed on Tuesday that Lebanon will boycott “Friends of Syria” international conference that will be held in Tunis this week.

“In harmony with our decision to disassociate Lebanon from developments in Syria, we will not join the conference in Tunis,” Mansour told OTV.

Russia on Tuesday said it will not attend an international conference in Tunis this week aimed at seeking political change in Syria because the meeting only supported the opposition's cause.

The meeting was called "for the purpose of supporting one side against another in an internal conflict," the foreign ministry said in a statement. "We cannot accept the offer to attend this meeting."

Top Republican U.S. Senator John McCain called on Monday for Syria's opposition to be given weapons to help "defend themselves" against President Bashar al-Assad's forces, while excluding direct U.S. aid.

"I'm not calling for the direct supply of weapons by the United States of America," he told a news conference in Cairo.

The Red Cross said on Monday it was negotiating with the Syrian authorities and opposition fighters to try to bring a halt to violence in the country so it can deliver vital aid.

"The International Committee of the Red Cross is exploring several possibilities for delivering urgently needed humanitarian aid," said spokesman Bijan Farnoudi.

The Phalange Party criticized on Monday the current crisis in the government, saying that it has demonstrated that it is incapable of settling the smallest of disputes.

It said in a statement after its weekly politburo meeting: “The solution to the crisis should adhere to the constitution and respect the role of the president and prime minister.”

President Bashar al-Assad said on Monday that foreign parties were funding "armed terrorist groups" to destabilize Syria and intent on blocking any political solution, the state news agency SANA reported.

It said the embattled president made the accusation in a meeting with a visiting top Russian MP, Alexei Pushkov, head of the international affairs committee of Russia's lower house of parliament.

Violence killed 15 people across Syria on Monday as regime troops massed around Homs, sparking calls for women and children to flee the besieged flashpoint city, as Iranian warships docked at the port of Tartus in a show of force.

The reported buildup came as Mediterranean states meeting in Rome agreed to preserve Syria's territorial integrity and avoid an "Iraqi scenario," according to Tunisian Foreign Minister Rafik Abdessalem.

Syria's opposition is expected to take part in an international conference in Tunis on Friday to which European Union and Arab League members as well as China, Russia and United States have been invited.

Speaking after a meeting of Mediterranean region foreign ministers in Rome on Monday, Tunisian Foreign Minister Rafik Abdessalem also said the talks had agreed on the need to avoid "an Iraqi scenario" and preserve Syria's integrity.