Syrian rights activists say pro-government forces have killed at least 35 people as Damascus defied another Arab League deadline to let observers into the country to verify a government pledge to stop cracking down on dissent.

The activists say most of Sunday's killings by Syrian troops and pro-government militiamen happened in the central province of Homs, a hub of a nine-month pro-democracy uprising against autocratic President Bashar al-Assad. Activists say the dead include a father and three of his children. There was no independent confirmation of the casualties.

Activists say Syrian authorities also detained prominent dissident blogger Razan Ghazzawi at the Syrian-Jordanian border as she was traveling to Amman to attend a regional conference on press freedom. She is the latest of thousands of dissidents to be arrested in the government crackdown.

The Arab League had demanded that Syria authorize the entry of an observer mission from the bloc by Sunday or face new sanctions, but Damascus gave no sign of accepting the ultimatum. Syrian Foreign Ministry spokesman Jihad Makdissi said only that his government was still “exchanging messages” with the League about the observers.

Syria has complained that a large observer mission would undermine its sovereignty.

Syria says it is fighting terrorists who have attacked civilians and security forces. It has warned that any foreign intervention in the unrest will spread chaos throughout the region.

U.S. Vice President Joe Biden played down that warning Sunday. Speaking to reporters after talks with Turkish leaders in Istanbul, he said the United States and Turkey believe the Syrian uprising can be resolved with any violence being contained within Syria, and with Syrians managing their own transition of power.

Another senior U.S. official accused President Assad of forcing his minority Alawite sect into a deadly conflict with other sectarian groups. Speaking on a visit to Amman, Assistant Secretary of State for Near Eastern Affairs Jeffrey Feltman also accused Syria's ally Iran of being “actively engaged” in supporting Mr. Assad's crackdown on dissent and “facilitating” the murder of Syrian people.

It is not clear what additional measures the Arab League may take against Syria after Damascus missed Sunday's deadline to accept observers.

The 22-member regional bloc suspended Syria's membership and approved a series of sanctions last month, including travel bans and asset freezes on the Syrian leadership. Arab League ministers who met in Doha Saturday agreed to impose the sanctions on 19 Syrian officials, including President Assad's brother Maher, who leads one of the military's most powerful divisions.

Other targeted officials include Syrian Cabinet members and Mr. Assad's cousin and telecom tycoon, Rami Makhluf. The president himself was not on the list.