Bahrain has stepped up its crackdown on anti-government protesters (almost all of whom are (Shia Muslims) by arresting at least 300 activists in one massive sweep, thereby sending untold others into hiding. Those detained included a prominent blogger, Mahmood al-Yousif.

The opposition has described the detentions as a campaign of terror.

The situation is critical. Almost all the bloggers and activists who aren't in jail are now in hiding, Nabeel Rajab, head of the Bahrain Centre for Human Rights, told Al Jazeera.

Rajab also told other media: The last few nights they been raiding houses and beating and arresting people. Some people were also arrested at checkpoints controlled by thugs brought in from other Arab and Asian countries -- they wear black masks in the streets.

The Sunni ruling al-Khalifa dynasty of Bahrain appears to be taking an increasingly hard-line against protesters. They have already imposed a temporary martial law (giving state security forces wider powers to arrest) and invited troops provided by Saudi Arabia (a Sunni-dominated power) to quell disturbances in the country.

The government says it is taking steps to ensure stability and security, but what's happening is the exact opposite, Mattar Ibrahim Mattar, of the Shia opposition group Wefaq, told Al Jazeera.

We're in one of the most dangerous stages, where citizens have no security. They're being arrested and kidnapped at checkpoints that are all over Bahrain. The checkpoints are a place of fear.

The presence of foreign troops on Bahraini soil has outraged not only opposition groups within the country; but also Iran (a regional Shia power).

Sunni-ruled nations, particularly Saudi Arabia, are wary of Iranian activities in the Persian Gulf Arab states.

Separately, Hezbollah, the Lebanese Shia militant group, has denied accusations by the Bahraini government that it has provided military training to Shia Bahraini protesters.

Earlier, Sheikh Khaled bin Ahmed Al Khalifa, Bahrain's foreign minister, told the Al Hayat newspaper on Wednesday that Hezbollah had trained Bahraini elements in Lebanon. He also described Hezbollah as a terrorist group.

We have to affirm that our Bahraini brothers did not ask us for any military or security training on any day and we have not given any training of that kind, Hezbollah said in a statement.

However, it is true that Hezbollah has offered help to their fellow Shias in Bahrain. In a recent speech that was televised, Hezbollah’s chief Sayyed Hassan Nasrallah, offered support to the Bahraini protesters in Bahrain, without providing any details.

In response, the Bahrain government formally protested to Beirut.