Syrian security forces have raided and sealed the Damascus office of Hamas chief Khaled Meshaal, who left the city months ago along with other leaders of the Palestinian Islamist group, Hamas said on Wednesday.

Relations between Hamas and long-time ally Syria have soured since Meshaal and other senior officials quietly quit Damascus late last year after President Bashar al-Assad stepped up a crackdown on anti-government protests.

Syria is home to at least 500,000 Palestinians, according to the United Nations. Syria's uprising has split loyalties, with many Palestinians sympathetic to the 19-month-old uprising by their fellow Sunni Muslims, and others backing Assad, whose Alawite faith derives from Shi'ite Islam.

In recent weeks, dozens of Palestinians have been killed by Syrian army shelling of rebel positions in and around the Yarmouk refugee camp in Syria, opposition campaigners said.

Meshaal's office, which had also served as his residence and the group's main headquarters in Damascus, was raided on Monday, Hamas said in a statement.

It said government forces confiscated property and sealed the building, which had been guarded by Hamas members.

Syrian security services closed the Damascus office of Emad al-Alami, a senior Hamas political official, on Tuesday, the statement said. Alami is currently in the Gaza Strip, an enclave Hamas has controlled since 2007. Meshaal's whereabouts are unknown.

Meshaal had been based in Damascus since 2001. Syria became a safe haven for him and other Hamas officials, who could have faced Israeli attack in the Gaza Strip, a territory closely monitored by Israel and under an Israeli blockade.

Israel, the United States and the European Union have classified Hamas as a terrorist organisation and shun the group over its refusal to recognise Israel, renounce violence and accept existing interim Israeli-Palestinian peace agreements.

Hamas angered Assad last year when it rejected pressure from the Syrian leader to hold a rally in his support in Damascus.