The fallout from Islamic State's attacks in Iran's capital Tehran has continued with revelations that gunmen and bombers were Iranian members of IS who had fought in the militants' strongholds in Syria and Iraq – deepening the regional ramifications of the assaults.

The attackers raided Iran's parliament and Ayatollah Khomeini's mausoleum on Wednesday morning, in a rare strike at the heart of the Islamic Republic. Authorities said the death count had risen to 17 and scores were wounded.

Iran's powerful Revolutionary Guards have also said regional rival Saudi Arabia was involved, fuelling tensions between the two nations as they vie for influence in the Gulf.

However, for one Iranian priest it is prayer that counts now.

Rev Hormoz Aslani Babroudi, national director of the Pontifical Mission Societies, told the Fides news service: 'As an Iranian Assyrian Chaldean Catholic priest, I am saddened by such inhumane acts, mostly accomplished by people who present themselves as faithful to God and Islam, and therefore spread a false image of faith and religion.'

He said: 'The perpetrators of the massacres do not know that these acts will fail to spread fear among the people or weaken the state: so many have tried to do it before them, and they did not succeed, and they will not succeed this time and in the future. Because Iranian, Muslim, and Christian people will always be united in defending the principles of their faith and their country.'

He expressed his condolences to 'spiritual guide', Ayatollah Ali Khamenei – Iran's Supreme Leader – and President Hassan Rouhani, and said: 'I will pray for the souls of those who have lost their lives, for the comfort of their family members and also of all the wounded'.

US President Donald Trump said on Wednesday he was praying for the victims, but added that 'states that sponsor terrorism risk falling victim to the evil they promote'.

Foreign minister Mohammad Javad Zarif dismissed what he called the 'repugnant White House statement'. 'Iranian people reject such US claims of friendship,' he added on Twitter.

Additional reporting by Reuters.