Shocked! For once Iran may actually have it right! This is an internal issue, let the people of Bahrain deal with these issues themselves!
Iran has denounced the use of troops from neighbouring Gulf states in Bahrain as "unacceptable".
Some 1,000 troops from Saudi Arabia and a further 500 from the United Arab Emirates arrived in Bahrain on Monday at the invitation of the government.
The US state department has urged its citizens to avoid travelling to the country due to the ongoing unrest.
Protesters have blocked all roads leading to the capital's financial centre, the scene of clashes on Sunday.
Iran - the main Shia power in the Gulf - has said that the arrival of the foreign troops is an "interference".
"The presence of foreign forces and interference in Bahrain's internal affairs is unacceptable and will further complicate the issue," Foreign Ministry spokesman Ramin Mehmanparast said.
"The people of Bahrain have demands, which are legitimate and are being expressed peacefully," he said.
"Any violence in response to these legitimate demands should be stopped."
The BBC's Caroline Hawley, in Manama, said that in the financial district demonstrators have built barricades from upturned rubbish bins, and many are wearing masks to protect themselves from tear gas.
The protesters are demanding widespread political reforms in the kingdom. The Shia Muslim majority has long complained of discrimination and dominance by the Sunni minority, including the ruling royal family.
The Shia-led opposition has said that the arrival of Gulf states troops - the first time that any Arab government has called for outside military help during the current wave of protests sweeping the region - is tantamount to a declaration of war.
The troops are part of a deployment by the Gulf Co-operation Council, a six-nation regional grouping which includes Bahrain, Saudi Arabia, Kuwait, Oman, Qatar and the United Arab Emirates.
It is believed they are intended to guard key facilities such as oil and gas installations and financial institutions.