|Television footage showed Saudi troops entering Bahrain in armoured vehicles [REUTERS]
Hundreds of Saudi troops have entered Bahrain to help protect government facilities there amid escalating protests against the government.
Bahrain television on Monday broadcast images of troops in armoured cars entering the Gulf state via the 26km causeway that connects the kingdom to Saudi Arabia.
The arrival of the troops follows a request to members of the Gulf Co-Operation Council (GCC) from Bahrain, whose Sunni rulers have faced weeks of protests and growing pressure from a majority Shia population to institute political reforms.
The United Arab Emirates has also sent about 500 police to Bahrain, according to Abdullah bin Zayed Al-Nahyan, the Emirati foreign minister.
The US, which counts both Bahrain and Saudi Arabia among its allies, has called for restraint, but has refrained from saying whether it supports the move to deploy troops.
"We urge our GCC (Gulf Co-operation Council) partners to show restraint and respect the rights of the people of Bahrain, and to act in a way that supports dialogue instead of undermining it," Tommy Vietor, the White House spokesman, said.
Interestingly, the Pentagon said neither Gates nor Admiral Mike Mullen, chairman of the Joint Chiefs of Staff who also recently visited Bahrain, had been given any indication that Saudi or other forces from the region would deploy to Bahrain.
Iran, meanwhile, has warned against "foreign interferences".
"The peaceful demonstrations in Bahrain are among the domestic issues of this country, and creating an atmosphere of fear and using other countries' military forces to oppress these demands is not the solution," Hossein Amir Abdollahian, an official from the Iranian foriegn ministry, was reported by Iran's semi-official Fars news agency as saying.
Abdel al-Mowada, the deputy chairman of Bahrain's parliament, told Al Jazeera that it was not clear how the Saudi force would be deployed but denied the troops would become a provocation to protesters.
"It is not a lack of security forces in Bahrain, it is a showing of solidarity among the GCC," he told Al Jazeera.
"I don't know if they are going to be in the streets or save certain areas ... [but protesters] blocking the roads are no good for anyone, we should talk.
"The government is willing to get together and make the changes needed, but when the situation is like this, you cannot talk."
The Saudi troops arrived less than 24 hours after Bahraini police clashed with demonstrators in one of the most violent confrontations since troops killed seven protesters last month.
Opposition groups, including Wefaq, the country's largest Shia movement, have spoken out against the use of foreign troops.
"We consider the entry of any soldier or military machinery into the Kingdom of Bahrain's air, sea or land territories a blatant occupation," Wefaq said in a statement.
'Urgent distress call'
Speaking to Al Jazeera from Bahrain, Matar Ebrahim Matar, an opposition MP, said: "These are not security forces, they are military forces. There is a big difference between the two.
"The fact is, they are coming with those military forces to face unarmed people in Bahrain, and that is the reason Bahrainis are sending an urgent distress call to the UN through their political parties.
"The political parties are supporting the dialogue, and they are waiting for initiatives from Crown Prince Salman [bin Hamad Al-Khalifa]. But the government has not provided any proposal. Until now all the terms set by the royal family are vague."
Nabeel Rajab, from the Bahrain Centre for Human Rights, told Al Jazeera that the Saudi troops would be opposed by the protesters.
"This is an internal issue and we will consider it as an occupation," he said. "This step is not welcomed by Bahrainis. This move is not acceptable at all. It is a repressive regime supported by another repressive regime."
Already, as reports circulated about the Saudi force's arrival, hundreds of protesters had gathered behind makeshift checkpoints around the Pearl Roundabout, the scene of much of the protest in Bahrain.
Nevertheless, in a sign that the opposition and Bahrain's royal family could still find a solution, the opposition groups said they had met the crown prince to discuss the mechanism for national dialogue.
Salman offered assurances on Sunday that dialogue would address key opposition demands, including giving parliament more power and reforming government and electoral districts.
Qatari PM's remarks
Speaking to Al Jazeera about Monday's Gulf troop deployment, Sheikh Hamad bin Jassim bin Jabr Al-Thani, the Qatari prime minister and foreign minister, said: "There are common responsibilities and obligations within the GCC countries.
"The arrival of Saudi and UAE troops in Bahrain is in line with a GCC defence agreement that calls for all members to oblige when needed and to fully co-operate."
He did not rule out the possibility of a Qatari presence, saying: "To be honest, we always have had Qatari peacekeeping troops. We have troops in Eritrea [in east Africa] to keep the peace between that country and Djibouti.
"We are committed to adhering to the GCC agreement. At the moment we have peacekeeping troops. We don't have a full force there, but this is up for discussion.
"What I want to say is that the situation is Bahrain is very sensitive and we wish that peace will prevail in the streets of Bahrain. I think that the call from the next-in-line to the throne in Bahrain for dialogue is a sincere call, and should be regarded seriously by all sections."
Sheikh Hamad bin Jassim said "if we want the talks and dialogue to succeed, then we need to calm the situation in the streets. This can be achieved by the withdrawal of everybody from the streets."
Referring to the Bahraini Shia parties' opposition to the military intervention, he said: "As I said, dialogue is the only way to solve everything, and this cannot be achieved under the tense circumstances. Therefore I advise the protesters to retreat. This is a genuine invitation that will lead to a serious dialogue that will lead to concrete results in Bahrain."