British police arrested two additional men Monday afternoon in connection with the failed car bombings in London and Glasgow.

Police in Scotland said two men, aged 28 and 25, were being held in connection with the attempted car bombing of Glasgow airport Saturday.

The men are not believed to be of Scottish origin. The arrests were the result of "intensive police operations" in Paisley, a small town near Glasgow.

The arrests bring the number of people held over the three attacks to seven.

Surveillance needed

Britain has some of the most extensive video surveillance in the world, and Germany needs to follow suit by installing more video surveillance in large cities, German Interior Minister Schäuble said in a television interview Sunday.

"I think that this is fundamentally important," Schäuble said.

Surveillance is already being used in places where the federal government has control over security, such as in train stations and airports, he added. Regional police have to decide how far to go with video monitoring in cities, Schäuble said in a radio interview Monday.

Terrorism attacks can only be prevented when terrorists' intentions are known, Schäuble said.

Islamist terrorists have Germany in their sights, said Konrad Freiberg, president of Germany's police union.

"We must count on strong attacks on us in the near future," Freiberg said in an article published in the Passauer Neuen Presse newspaper Monday.

French officials discuss attacks

France is also on high terror alert after senior officials met Sunday to discuss how to best react to the attempts in Britain.

"It is obvious that France, like a number of other countries, is a potential target of terrorism," French Interior Minister Michele Alliot-Marie told reporters following the meeting.

France kept its terrorist level at its second highest, "red." The highest level is "scarlet."

French President Nicolas Sarkozy sent a note to British Prime Minister Gordon Brown, offering help in the investigation.

"In this implacable fight against terrorism, our countries are not only unfailingly united, but also in close and constant cooperation," Sarkozy said in the note sent Saturday.

British investigation continues

In Britain, police warned travelers to expect delays at airports and train stations. Controls and searches of cars were being increased amid fears of further attacks.

Police said they have found links between two cars filled with gas canisters and nails in London's entertainment district Friday and a Jeep which rammed into the Glasgow airport Saturday.

Police anti-terror chief Peter Clarke told reporters in Glasgow that the investigation was "extremely fast-moving" and added that the links between the three attacks in London and one in Glasgow were becoming "ever clearer."

Police have said the suspects are not British, with news reports saying one is Iranian. Scottish government leader Alex Salmond said two suspects caught in the attempted Jeep bombing of the Glasgow airport had "not lived in Scotland for long."

One of the two suspects in the Glasgow attack remains in critical conditions with severe burns at a nearby hospital. He is under armed police guard.

British Home Secretary Jacqui Smith said it was "speculation" to talk about the nationalities of the suspects.

"We can't know, for example, everything about the identities of those who have been arrested," Smith said Monday in an interview with Sky News.

Smith said she was encouraged by the progress made in the investigation. She was scheduled to update lawmakers on the probe on Monday.

US wants more checks on Europeans

US President George W. Bush praised Brown's "very strong response" to the attempted attacks, and US Homeland Security head Michael Chertoff said the US takes the threat in Britain seriously and added that extra air marshals will be deployed on flights to Britain.

Additionally, the US wants to further increase checks on people traveling from Europe to the States, he said.

"It's one of the reasons we've been very focused on increasing our security for people incoming from Europe," he said. "And that's something we're going to be looking at for the rest of the summer."