Syria's opposition urged the Arab League to immediately send observers to Homs and other areas where Syrian forces are reported to be killing dissenters. The central-western city, a focal point of the Assad regime's crackdown on anti-government demonstrations, is "under a tight siege" with an imminent "threat of military invasion by an estimated 4,000 soldiers," the Turkish-based Syrian National Council said in a statement. "This is in addition to the non-stop bombing of Homs that has been going on for days," said the chief umbrella group of opponents of embattled President Bashar Assad. The appeal came as the Local Coordination Committees activist network reported at least 13 people, including three children, were killed and scores injured Sunday in the regime's crackdown. The violence Sunday included "random shelling," heavy gunfire and house torching in Homs by loyalist forces, the network said. Security forces arrested 26 people in one neighborhood and made them strip down to humiliate them, the committees said. Journalists are heavily restricted in Syria and it was impossible to verify the activists' accounts. The appeal also came as a delegation of about 50 Arab League observers was to arrive in Syria Monday. The delegation, led by Sudanese Gen. Mohammed al-Dabi, planned to meet with various Syrian groups, including Assad military and opposition members, Dabi said in remarks carried by Egypt's official Middle East News Agency. The league is based in Cairo. The observers, who started arriving in Syria last week, are charged with monitoring regime compliance with its pledges to withdraw troops from besieged areas and implement an Arab League peace agreement signed by Syrian officials. About 150 monitors will eventually monitor the compliance and they will likely determine within a week if the Assad regime is implementing the peace agreement, the league said. Pope Benedict XVI, in his Christmas message, called for God to "bring an end to the violence in Syria, where so much blood has already been shed." The United Nations says at least 5,000 people have died in the Syrian conflict. Human rights group Avaaz, which helps document protests, said Thursday it collected the names of 6,237 people who had been killed, including more than 800 women and children and 917 loyalist troops. Syrian state news agency SANA said Thursday more than 2,000 Syrian security force members had been killed since anti-regime uprising broke out March 17.