Syrian forces on Tuesday pounded protest hubs in apparent breach of a ceasefire deal brokered by U.N.-Arab League envoy Kofi Annan, who appealed for his plan to be implemented without preconditions.

Syria said it was abiding by the plan, but Annan accused Damascus of pulling troops from some areas and moving them to others, and the rebel Free Syrian Army warned it would resume attacks if the government offensive does not stop.

U.N. and Arab League envoy Kofi Annan will send a letter to the Security Council Tuesday on Syria, his spokesman said, the day a U.N.-Arab plan to end 13 months of bloodshed is to take effect.

"Mr. Annan will be sending a letter to the Council later today," spokesman Ahmad Fawzi told Agence France Presse.

Shots fired from Syria at a Syrian refugee camp inside Turkey are a "clear violation" of the common border between the two countries, Turkish Prime Minister Recep Tayyip Erdogan said Tuesday.

"It was a very clear violation of the border," Erdogan told reporters in Beijing, where he is on an official visit. "Obviously we will take the necessary measures," he was quoted as saying by the Turkish news agency Anatolia.

U.N. leader Ban Ki-moon on Monday “strongly” deplored the fatal cross-border shootings from Syria into Lebanon and Turkey earlier in the day, U.N. spokesman Martin Nesirky said in a statement.

Ban also made a final plea for President Bashar al-Assad to halt attacks on civilians ahead of a Tuesday deadline to withdraw troops and heavy guns from Syria's cities.

Two Syrians among a group of 17 who were wounded when their village was shelled overnight died after crossing the border into nearby Turkey, an official said Monday.

Two other Syrians and a Turkish translator were wounded near a refugee camp in the same area when shots were fired from Syria, as border tension escalated ahead of a visit by top international mediator Kofi Annan.

The international mediator for Syria, Kofi Annan, was due in Turkey Tuesday for a visit to Syrian refugee camps near the border, a Turkish diplomatic source said Monday.

"The visit will only last a few hours, ahead of Annan's trip to Iran," the official told AFP on condition of anonymity.

Turkey's prime minister has warned of as yet unspecified "steps" if the government of neighboring Syria fails to abide by an April 10 deadline to cease violence, local media reported on Sunday.

"We will patiently follow the process until April 10," Recep Tayyip Erdogan was quoted as saying by daily Hurriyet.

The Organization of Islamic Cooperation chief on Saturday welcomed a request by the self-proclaimed Turkish Republic of Northern Cyprus to open a permanent mission to the pan-Muslim body.

"The organization welcomes this and is in contact with the host state (Saudi Arabia) to study and implement it," OIC chief Ekmeleddin Ihsanoglu, who is a Turkish national, told reporters after meeting Turkish Cypriot leader Dervis Eroglu.

Turkey's Prime Minister Recep Tayyip Erdogan was leaving Saturday for the first official visit to China by a Turkish premier in 27 years, an aide from his office told Agence France Presse.

Erdogan will first make a stopover in China's far-west Xinjiang Uighur autonomous region, the aide said Saturday speaking on condition of anonymity.

Nearly 700 Syrian refugees poured into Turkey in 24 hours, bringing to more than 24,000 the total number of Syrians seeking haven in the neighboring country, a Turkish official said on Saturday.

Turkey is home to a growing number of refugees fleeing the unrest in Syria, where more than 9,000 people have been killed since March last year, according to U.N. figures.