BEIRUT - For years, websites linked to Iran's Revolutionary Guard have posted articles eulogising fighters who die in Syria. But two men heralded last month for dying to defend a shrine near Damascus were different from most martyrs given such treatment in the past: they were Pakistanis.

The men were part of the Zeinabiyoun, a unit of Pakistani fighters named for a granddaughter of the Prophet Muhammad (PBUH) buried in the shrine.

The increase in the number of "martyrdom" notices of fighters from the group this year indicates they are taking a more active role in the conflict. A posting in mid-November on a Twitter account bearing the group's name displayed the pictures of 53 men, described as fighters killed in battle.

While there has been no official announcement of their total numbers, a regional source familiar with the issue said there were hundreds of Pakistanis fighting in Syria, many stationed around the shrine of Zeinab.

Iran's recruitment of the Pakistani fighters adds yet another international dimension to Syria's 4-year-old civil war.

The Pakistani Shi'ites are helping to defend the government of Tehran's ally, President Bashar al-Assad, who is also supported by Russian air strikes and fighters from Lebanon's Hezbollah militia, against an array of Sunni rebels backed by Turkey and Arab states. The United States, Turkey, Arab and European powers are also participating in a coalition bombing Islamic State, a Sunni militant group.

A Facebook page bearing the name of the Zeinabiyoun showed pictures of what was described as a funeral in Iran in late November, with members of Iran's Revolutionary Guard standing next to men in shalwar kameez, the traditional long tunic and trousers worn in Pakistan.

"The Zeinabiyoun are a Pakistani Shi'ite outfit that's run by the IRGC," said Phillip Smyth, a researcher at the University of Maryland and adjunct fellow at the Washington Institute for Near East Policy who has done extensive research on Shi'ite groups fighting in Syria, using an acronym to refer to Iran's Islamic Revolutionary Guard Corps.

"They've put together their own imagery, their own recruitment type material. They really became more of a marketable element toward the end of the summer of 2015. That's when they became more of a centred group."

They are only the latest Shi'ites recruited by Iran to fight in Syria, after Hezbollah fighters from Lebanon, members of Iraq's Shi'ite majority and members of Afghanistan's ethnic Hazara Shi'ite minority. All have been deployed to support Assad, whose own Alawite sect is an offshoot of Shi'ite Islam.

Videos and pictures posted on social media sites say Zeinabiyoun fighters have been active around Aleppo as well as at the shrine near Damascus in the last month.

Based on material posted online, the Zeinabiyoun could have up to 1,000 fighters, estimated Smyth.

Attempts to get comment from a public relations news office of the Revolutionary Guard were unsuccessful.

According to the group's postings on the internet, some of the Pakistanis fighting in Syria were already residing in Iran, while others come from a community of Pashtun Shi'ites in the town of Parachinar in the Pakistani tribal areas.

The Zeinbayioun started out as part of a unit of Afghan fighters called the Fatemiyoun, Smyth said. The Fatemiyoun have taken heavy losses in Syria and there are regular postings about their casualties on hardline Iranian sites.

One recruitment ad posted on Facebook last week said any physically fit man between 18 and 35 should apply to fight in Syria. It offered 45 days of initial military training along with six months of further training in Syria, a salary of 120,000 Pakistani rupees (approximately $1100) per month and 15 days of holiday every three months.

If the recruit is killed in action, his children's education will be paid for and the family will be given pilgrimage trips to Iran, Iraq and Syria every year. Any willing recruits should make their way to Iran's holy city of Qom, the ad said. A phone number was provided. There was no answer when Reuters rang.

The Afghan and Pakistani recruits help make up for the withdrawal of Iraqi Shi'ite militia units, called home to help fight Islamic State fighters there last year.

"It's clear that they (Afghan and Pakistani recruits) had to accept that role from the Iraqi Shi'ites who were pulled out," Smyth said.