BERLIN -- An attempted arson attack on a railway link in Germany's capital with three separate explosives devices was thwarted Monday, police said. It was the third in two days targeting railway operations in and around Germany's capital.

A railway employee found the explosive devices placed on cables along a railway track in eastern Berlin on Monday morning and alerted security, police spokesman Ivo Habedank said.

The devices did not explode and were defused by police experts. It was not immediately clear how much damage they would have caused, but there are no houses or busy streets nearby, Habedank said.

Parts of Berlin's train services to and from the city's southeast were halted for more than two hours due to the incident, he added.

An arson attempt Monday on Berlin's central station using seven bottles filled with flammable liquid bundled together and linked to a fuse was thwarted at the last minute. A similar device exploded in a utility shaft next to a high-speed train line west of Berlin a few hours earlier, causing damage but no casualties, and halting train traffic there for the day.

It was still unclear whether the attacks were related, Habedank said.

A previously unknown leftist group claimed responsibility for Monday's attacks in a letter whose authenticity was being examined by police.

In a message posted on a leftist website, a group calling itself Hekla Reception Committee -- Initiative for more Eruptions in Society claimed responsibility, saying it was targeting railway operations to protest Germany's roles in the Afghanistan war and as an arms exporter. The group's name is an apparent reference to Iceland's Hekla volcano.

Berlin has seen several recent arson attacks that police have blamed on leftist extremists.

One of them in May targeted a utility shaft at an important railway hub in the city's east, causing massive disruption that left thousands of passengers stranded.

Germany is a large contributor to the NATO-led International Security Assistance Force in Afghanistan, with about 5,000 soldiers stationed in the north of the country.