BEIRUT (Reuters) - The Free Syrian Army rebel alliance said on Wednesday it would respect an Eid holiday ceasefire, but only if government forces also abided by it, accusing the government of having already violated the truce.

"We, the armed revolutionary groups in Syria, welcome any effort towards a ceasefire for the happy Eid al-Fitr period. We declare we will abide by it so long as the other side does the same," said the statement, posted on the Twitter account of Mohammed Alloush, the former chief peace negotiator for Syria's mainstream opposition.

"Until now, (the government) has not abided by what it has announced, in that it has launched a number of attacks in various areas today," the statement said.

Alloush is also the representative of the powerful Jaish al Islam rebel faction in the opposition High Negotiations Committee (HNC).

The Syrian government earlier declared a three-day ceasefire across the whole of the country, although fighting continued and until now there had been no indication that it had been agreed with any of the myriad groups opposing the government.

The truce is the first to be declared country-wide since one was brokered by foreign powers in February to facilitate talks to end the five-year-old civil war. This has mostly unraveled.

The statement said the rebel alliance welcomed international efforts that had led to the announcement from the government of Syrian President Bashar al-Assad, but that attacks had not ceased as a result.

Jaish al Islam spokesman Islam Alloush said: "The regime has made this announcement purely to escape international pressure. On the ground, I don't think anything has changed."

(Reporting by Lisa Barrington; Editing by Kevin Liffey)