(CNN) -- Syria faced additional sanctions from its Arab League neighbors Monday unless it agreed to allow international observers into the country to monitor an agreement to end a months-old crackdown on anti-government protesters.
As a midnight Sunday (5 p.m. ET) deadline passed, there was no immediate indication that Syrian officials had responded to the ultimatum. Syria's state-run news agency said the country could withstand sanctions already imposed by the Arab League and by neighboring Turkey, and human rights and opposition groups said at least 22 more people were killed as the clampdown continued.
Over the weekend, Arab League officials meeting in the Qatari capital Doha responded to requests by Damascus for some clarifications to the plan, but did not make any key changes, according to Qatar's foreign minister, Hamad bin Jassim al-Thani. Ministers agreed over the weekend to freeze the assets of more top Syrian officials, reduce flights in and out of the country by half and impose a complete ban on weapons shipments to Syria, a statement from the Arab League said.
"You saw yesterday human rights abuses, and this keeps building up," al-Thani said over the weekend. "Our mission is that none of these abuses continue anywhere in the Arab states, including Syria."
He warned that the Syrian crisis could be "internationalized" unless the government of Bashar al-Assad complies with a deal to end its clampdown on opposition. Syria agreed in November to halt all violence, release all detainees, withdraw all security forces from populated areas and allow unfettered access to the nation by journalists and Arab League monitors -- but opposition groups say assaults by government troops and police have continued, and no monitors have been put in place.
The Arab League responded by announcing economic sanctions in late November. But Ahmed Hamoudi, general coordinator of the Egypt-based Syrian Revolution Coordination, expressed skepticism about whether the sanctions would help end al-Assad's 11-year rule.
"The economic sanctions by the Arab League serve a good purpose of pressuring the Syrian regime and weakening it, but I don't think the Arab League will be able to fulfill the political ambitions of the Syrians -- and that is to topple the Assad regime," Hamoudi said.
"We want to see the Syrian file taken to the U.N. Security Council and more immediate measures on the ground, like a no-fly zone and a buffer zone at the Turkish border."
The United Nations estimates that more than 4,000 people have died since mid-March, and the death toll continues to rise. The Local Coordinating Committees of Syria, an opposition umbrella group, said 22 people had been killed Sunday. All but one of the deaths occurred in the city of Homs, the scene of much of the recent unrest, the group said.
The London-based Syrian Observatory for Human Rights put the toll at 40, including five soldiers who had defected and taken up arms against the government. The deaths included 26 in Homs, three in the suburbs of Damascus and six in Idlib, near the Turkish border.
An opposition website based in Idlib reported clashes between military defectors and Syrian troops on a highway. Two defectors and an army colonel were killed, the website said.
CNN could not independently confirm the accounts, since the Syrian government has limited access to the country by international reporters.
Arab League sanctions already imposed in November include cutting ties with Syria's central bank, banning high-profile Syrian officials from visiting Arab nations and freezing the assets of the Syrian government, according to a senior league official who asked not to be named because he was not authorized to speak to the media.
In a statement issued late Sunday, the state-run Syrian Arab News Agency said the nation would survive the sanctions being imposed on it by its neighbors.
"Although they will affect the livelihood of Syrian citizens, Syria will overcome those sanctions by virtue of its strategic location and the diversity of its production sectors," the news agency said.
And it said Damascus was ending a free-trade agreement with Turkey and slapping a tariff on Turkish goods imported into Syria in retaliation for sanctions Turkey has imposed.
The number of deaths across Syria has reached at least 4,000 since the crackdown began in mid-March and could be much higher, Navi Pillay, U.N. high commissioner for human rights, said Thursday.
The uprising against al-Assad began in February. Demonstrations have continued across the country, with protesters demanding his ouster and democratic elections.
CNN's Saad Abedine, Yasmin Amer and Rima Maktabi contributed to this report.