The United States said Tuesday that persistent violence in Syria was "unacceptable" and demanded that President Bashar al-Assad do more to comply with a peace plan to end months of bloodshed.

State Department spokesman Mark Toner said that a ceasefire -- which went into force on Thursday -- was eroding due to the daily violence and said that the opposition was upholding its side of the peace deal.

U.N. observers acknowledged on Tuesday that they face a tough task to firm up a ceasefire in Syria, as more civilians were killed in the latest violence on the sixth day of a tenuous truce.

The Syrian Observatory for Human Rights said security forces killed five civilians, while the Local Coordination Committees, the main activist group spurring protests on the ground, said 66 civilians were killed across the country.

Libyan authorities have met resistance in talks for the handover of Seif al-Islam, the son of slain leader Moammar Gadhafi, who is still being held in Zintan, a negotiator told Agence France Presse on Tuesday.

Zintan officials told representatives of the ruling National Transitional Council that people in the town "want Seif to be tried locally because the (interim) government is weak," an NTC member said on condition of anonymity.

Qatari Prime Minister Sheikh Hamad bin Jassem al-Thani said Tuesday that no progress has been made to end Syria's deadly 13-month crisis.

"We hope the Syrian government responds" to U.N.-Arab League envoy Kofi Annan's six-point peace plan, Sheikh Hamad told an Arab ministerial meeting in Doha. "We don't see any progress in implementing" it.

Israeli Prime Minister Benjamin Netanyahu on Tuesday received a letter from president Mahmoud Abbas about the moribund peace process, as he met in Jerusalem with two Palestinian officials, his office said.

The brief meeting was described by the Palestinians as "serious," with both sides saying Netanyahu would reply with his own letter to Abbas "within two weeks."

A group of 50 countries supporting sanctions against Bashar al-Assad's Syrian regime on Tuesday issued a statement denouncing continued arms sales to Damascus.

After meeting in Paris, the countries expressed "strong disapproval of any financial or other support, in particular the continuation of arms sales to the Syrian regime", in a clear reference to Russia.

Egypt's electoral commission confirmed on Tuesday that 10 candidates have been barred from running for president, ruling out a challenge by two Islamists and Hosni Mubarak's ex-spy chief.

"The commission rejected all appeals presented by the 10" candidates among 23 who applied to stand in the election scheduled for next month, said the official MENA news agency.

The six Gulf monarchies meeting in Doha on Tuesday condemned as "provocative" a visit by Iranian President Mahmoud Ahmadinejad to an island claimed by both Abu Dhabi and Tehran.

The members of the Gulf Cooperation Council "strongly condemn the Iranian president's visit to Abu Musa which is a provocative act and a flagrant violation of the sovereignty of the United Arab Emirates over its three islands," they said in a joint statement.

France's Alain Juppe plans has invited several of his fellow foreign ministers to talks in Paris on Thursday on ways to boost the pressure on Bashar al-Assad's Syrian regime, a government source said.

The official said the meeting and the guest list were not finalized, but that Juppe hoped to host around a dozen ministers, some of whom will be in the region already for NATO talks in nearby Brussels on Wednesday and Thursday.

EU foreign affairs chief Catherine Ashton on Tuesday urged Bahrain to save a jailed activist on hunger strike whose health is now "a matter of the utmost urgency."

A day after protesters climbed onto the roof of the Bahraini embassy in London in support of Abdulhadi al-Khawaja, Ashton said there was "serious and profound concern" in the European Union about the case.