Activists say Syrian security forces mounted a major offensive in the port city of Latakia Sunday, with warship and tanks joining the assault.

Residents say at least six people have been killed since tanks rolled into the city on Saturday, a day after thousands of anti-government protesters rallied there. Two people were killed on Saturday and at least four more on Sunday.

A separate raid took place Saturday in the Qusair region, near the Lebanese border, where activists say at least one person was killed.

The unrest comes after security forces are reported on Friday to have killed at least 19 people across the country. Activists and witnesses say most of the deaths occurred after demonstrators took to the streets and renewed calls for President Bashar al-Assad's resignation.

Meanwhile, a report in an Israeli military magazine says Israel has planted new landmines along its border with Syria in an attempt to dissuade protesters from rushing into the Golan Heights.

Bamahaneh reports the new mines replace old ones that did not detonate earlier this year when protesters from two separate demonstrations in Syria crossed the border. Israel opened fire on the demonstrators, killing at least 35 people.

Media reports say Israel is concerned that planned Palestinian demonstrations in September around their U.N. bid for independence could also result in a new attempt to breach the Golan frontier.

Syrian President Assad has been facing growing international condemnation for his crackdown on dissent.

On Saturday, U.S. President Barack Obama and Saudi Arabia's King Abdullah called for an immediate end to the crackdown.

In a separate phone call, Mr. Obama and British Prime Minister David Cameron also agreed on the need for an “immediate” end to the bloodshed.

Canada announced Saturday that it is expanding economic sanctions against Syria.

Also Saturday, one of the world's largest Muslim inter-governmental organizations urged Syria to exercise restraint. The Organization of Islamic Cooperation also offered to play a role in dialogue in Syria.

The United Nations Security Council plans to meet on Thursday to consider further action against the Syrian government.

The Syrian government has blamed armed groups for much of the country's violence.

Details of events in Syria are difficult to independently verify because the government allows very few foreign news reporters into the country and restricts their movements.