DUBAI (Reuters) - Al Qaeda leader Ayman al-Zawahri has called on Muslims to kidnap Westerners, join Syria's rebellion and ensure Egypt implements sharia, SITE Monitoring reported, citing a two-part film posted on Islamist websites.

"We are seeking, by the help of Allah, to capture others and to incite Muslims to capture the citizens of the countries that are fighting Muslims in order to release our captives," he said, praising the kidnapping of Warren Weinstein, a 71-year-old American aid worker in Pakistan last year.

However, in a sign that al Qaeda could be under pressure, he said the release of the film had been delayed because of the "conditions of the fierce war".

Zawahri accused the international community of giving Syrian President Bashar al-Assad "a license to kill" in his attempts to smother a popular uprising. Syria's anti-government rebels include Islamist groups.

"I incite Muslims everywhere, especially in the countries that are contiguous to Syria, to rise to support their brothers in Syria with all what they can and not to spare anything that they can offer," he added.

The Egypt-born cleric directed questions towards the new Egyptian President, Mohammed al-Morsi of the Muslim Brotherhood, over his intentions towards Israel, Egyptian Christians and sharia law.

"The battle in Egypt is very clear. It is a battle between the secular minority that is allied with the church and that is leaning on the support of the army, who are made by (former president Hosni) Mubarak and the Americans... and the Muslim ummah in Egypt that is seeking to implement the sharia," he said.

He also used the two-hour, 12-minute address, posted on Islamist websites on Wednesday, to call U.S. President Barack Obama a "liar" and "one of the biggest supporters of Israel".

(Reporting By Angus McDowall; Editing by Myra MacDonald)