MOSCOW (Reuters) - A bomb destroyed an entire block of apartments in Moscow Monday, killing at least 45 people and prompting President Boris Yeltsin to order measures to tackle a growing terror campaign that has struck at the heart of Russia.

The eight-story building was razed, just four days after 94 people died in an eerily similar blast. Trees were splintered and masonry thrown over a wide area in a southern suburb. A children's play slide was visible in the rubble as drizzle added to the gloom.

Monday already was an official day of mourning for some 150 people killed in last Thursday's Moscow blast and another on Sept. 4 in Dagestan, a Russian region where Chechen-backed Islamic rebels have been battling Russian forces for weeks.

Yet the country again awakened to the news of an explosion and watched graphic footage of rescuers working by hand on a smoldering mound of rubble that was once an apartment block.

YELTSIN CALLS FOR CALM, VIGILANCE

``Today, a day of mourning, a new disaster hit us,'' Yeltsin said in a televised address. ``Terrorism has declared war on us, the people of Russia.''

He urged Russians to remain calm and vigilant and vowed a tough, swift response to those responsible. Prime Minister Vladimir Putin made similar remarks before he left an international summit in New Zealand to return urgently to Moscow on Yeltsin's orders.

``It's difficult even to call them animals,'' Putin said of those responsible. ``If they are animals, then they are rabid.''

No one has claimed responsibility for Monday's blast, nor for previous ones, which also included a bomb in a Moscow shopping mall that killed one woman and injured dozens of people. Officials have pointed the finger at Islamic militants.

The breakaway Russian republic of Chechnya and a leader of Islamic rebels in neighboring Dagestan denied involvement.

It is not clear why ``soft'' civilian targets have been chosen beyond an apparent desire to win maximum publicity and bring an otherwise remote conflict to the capital of the vast country.

In Moscow, visiting Defense Secretary William Cohen condemned the latest attack and told a news conference Washington would help Russia tackle the crisis.

Yeltsin said he had ordered increased security in key cities and at nuclear plants, fuel depots and other sites. He gave Moscow Mayor Yuri Luzhkov 24 hours to check airports, railway stations, cellars and attics across the capital.

PARTIAL, NOT GENERAL,
EMERGENCY MAY BE DECLARED

He said Luzhkov, a rival whose political alliance is likely to perform well in December's parliamentary election, would be given all the support he needed in tackling the bombing crisis.

``We are living amid a dangerous spread of terrorism and that demands the uniting of all forces in society and the state to repel this internal enemy,'' Yeltsin said.

The third explosion in two weeks fueled rumors the Kremlin was about to introduce a general state of emergency, a move that would cast into doubt the parliamentary election.

A Kremlin source told Reuters the Yeltsin meeting did not discuss such an option, although a Yeltsin aide said a partial state of emergency could be introduced in some parts of Russia.

The State Duma lower house of parliament asked Yeltsin and Putin to visit the chamber Tuesday to report on a crisis that has unnerved normally stoical Muscovites.

``I thought a war had broken out,'' said an elderly woman named Nina. ``I'm so scared, it's scary to walk home at night. And now they're bombing us in our beds.''

Four people were pulled alive from the wrecked building soon after the blast at 5:00 a.m. local time (9 p.m. EDT Sunday) Monday but since then only corpses, Emergencies Ministry officials said. They said four children were among the 45 dead.

``It is very unlikely we will find any more survivors,'' a rescue official told Reuters at the scene near the major Kashirskoye highway in southern Moscow.

Residents, crying and wide-eyed with fear, watched as bodies were dragged out. Books and clothes lay scattered on the ground and hung in branches of nearby trees.

Moscow police said they believed a man they are looking for in connection with Thursday's blast also rented a store in the block destroyed Monday. Police named him as Mukhit Laipanov and showed an artist's rendering of a dark-haired, bespectacled man. Officials later said a man of this name died some years ago.

A Russian newspaper said Monday a Chechen-led band composed mainly of ethnic Slavs was behind the series of explosions. The article in Novaya Gazeta gave no source.

``Of course we are taking serious measures,'' said Alexander Zdanovich, spokesman for the FSB domestic intelligence agency. ''But if we rely just on our forces it will not be enough because a real terrorist war is being waged.''