Syrian security forces have continued to crack down on dissent, activists say, as the opposition called for more protests to mark six months since the uprising began.

Dozens of tanks and hundreds of soldiers stormed towns and villages near Syria's northwest border with Turkey on Wednesday, local activists said.

At least four villagers were killed by security forces and thugs loyal to President Bashar al-Assad in the Jabal al-Zawiyah area, the activists said.

"This is an initial death toll. Communication with the region is very difficult," one activist said.

Armed with heavy machine guns, the forces cut off roads leading to several villages, setting up checkpoints and arresting several people, the UK-based Syrian Observatory for Human Rights (SOHR) said.

A boy was killed in the village of Janudiya when security forces opened fire to disperse protesters, the Syrian Revolution General Commission, a grassroots activists' organization, said.

SOHR also reported that one person was shot dead in the Bab Sbaa neighborhood in the central city of Homs.

Elsewhere, in the central region of Hama two people were killed when soldiers and security forces opened fire on them in the villages of Howeja and Bana, the group added.

Protesters defiant

Undaunted by the crackdown, protesters vowed to hit the streets en masse on Thursday to mark March 15, when people first took to the streets demanding reforms.

"Six months. More than ever determined to [continue] the March 15 uprising," activists wrote on Facebook page The Syrian Revolution 2011.

Earlier on Wednesday, several foreign ambassadors to Syria traveled to the Damascus suburb of Daraya to attend a condolence ceremony for a prominent slain Syrian activist.

Footage posted by activists on YouTube of the ceremony for Ghiyath Matar showed the ambassadors of the US Japan and France seated among others in an apparent show of solidarity with the anti-government protest movement.

Matar, a leading figure in protests that challenge the Syrian Baath party's 41-year-long rule, was killed under torture by authorities, according to activists. 

Hours after the visit by the envoys, government troops fired teargas at the gathering of mourners, activists said.

PHOTO CAPTION

New U.S. ambassador Robert Ford (R) talks with Syria's President Bashar al-Assad

Al Jazeera