ISLAMABAD, Pakistan (CNN) -- Pakistan's president praised his people Wednesday, calling Saturday's earthquake "a test for the nation" and requesting more international help as nuclear rival India joined the ranks of countries supplying aid.

Gen. Pervez Musharraf said some 23,000 people have been reported dead after the deadliest quake in South Asia for a century, and another 50,000 were injured.

Hours after Musharraf's televised address to the nation, a strong aftershock rattled buildings early Thursday in Pakistan's capital and the North-West Frontier province. No damage was reported.

The aftershock had a preliminary magnitude of 5.6 and was centered about 85 miles (135 kilometers) north of Islamabad, the U.S. Geological Survey said.

In the latest sign that Saturday's magnitude-7.6 quake could be easing tensions in the region, Indian troops Wednesday crossed the disputed line of control in Kashmir to help Pakistani soldiers repair a damaged bunker, an Indian army spokesman said.

The Indian soldiers were responding to a request for help from the Pakistani troops manning the bunker near the Aman Setu bridge, the only crossing between the regions of Kashmir controlled by Pakistan and India, the spokesman said.

The Indian defense ministry was working around the clock to clear the road to the bridge, also known as Kaman Bridge, which likewise was damaged in the quake, the spokesman said.

"Five to six soldiers from our side went across," the Indian army spokesman said.

India also sent a relief plane Wednesday to Islamabad carrying tents, medicines and other materials.

After initial reluctance, Pakistan decided to accept aid from India, with whom it has fought three wars -- two of them over the disputed Kashmir region that took the brunt of the quake.

Although India's Himalayan region suffered damage and casualties, Pakistani-controlled territory took the worst damage.

The earthquake killed at least 1,239 in India and one person in Afghanistan, according to government, police and hospital officials.

Some officials have said Pakistan's death toll could be nearer to 41,000. But Pakistani Foreign Minister Khurshid Mahmud Kasuri said Tuesday the government "can only give the number of the people actually certified as dead."

Millions homeless
Reaching the 2.5 million people the government says are now homeless is Pakistan's top priority, Musharraf said.

"Communication has broken down; roads are damaged," he said. "Telecommunications and electrical lines are destroyed."

With health experts warning the Himalayan region could become a fertile breeding ground for disease, Musharraf said food, medicine and shelter are the prime necessities.

Hundreds of millions of dollars worth of pledges have poured in from round the world, and the president thanked the international community for its response. But he said more help is needed, both financially and physically.

Particularly, he said, helicopters are needed to reach remote areas rendered accessible only by air.

U.S. Secretary of State Condoleezza Rice visited Pakistan after saying Washington would likely add to the $50 million it has committed to the quake recovery effort.

Pakistan is the latest stop on Rice's tour of Asia, which was expanded to include the earthquake-damaged nation. Rice met with Musharraf and Prime Minister Shaukat Aziz.

Pakistan has been a key ally in the U.S.-led war in neighboring Afghanistan.

Response defended
The United States has sent military helicopters from Afghanistan, and the number involved will grow substantially in the next few days, perhaps to several dozen, a senior defense official in Washington said Tuesday.

Rescuers have yet to reach some remote areas in the mountainous Pakistan side of Kashmir, and many bodies are still buried beneath piles of concrete, steel and wood. Hopes of finding more survivors were dimming.

The quake struck near Balakot, a city of about 250,000, 145 kilometers (90 miles) north-northeast of Islamabad.

In Muzaffarabad, the capital of Pakistan-controlled Kashmir, hungry survivors mobbed relief trucks loaded with food and water.

Severe weather has stymied relief efforts -- along with roads blocked by the quake itself.

Musharraf defended his government's response to the disaster -- a response some Pakistanis criticized as too slow -- saying the scope of the catastrophe made such problems unavoidable.

"Disaster is always painful, and the people who are still facing that are facing a very bad situation," he said. "In these dangerous situations, the easiest thing is to blame someone. Instead of blaming someone, we have to face it with confidence.

"We have to show that we have got the confidence, and we have got enough strength to face this," he said.

The president said relief efforts took some time to get started because the administrative structure in the affected regions collapsed and roads were impassable.

"I am very sorry for that delay," he said. "But there was no other way."

Many roads are now clear, he said, but other places remain inaccessible except by air.

"We need the strength to serve in this situation," he said. "This is a natural disaster, and nobody could predict this. The people who are gone are gone, but we can work for the future generations."

He said he could not praise the Pakistani people enough for jumping in and helping with relief efforts.

U.N. agencies report progress
Medical teams from throughout Pakistan and the world have rushed to the earthquake zone to treat injuries and prevent life-threatening infections.

Hans Strohmeyer, a United Nations senior humanitarian official, said Wednesday that access to the earthquake-affected areas of Pakistan has been increasing as the weather has improved. Clean water remains the key need, Strohmeyer said.

Many hospitals were damaged and many health workers were killed or injured in the quake, the World Health Organization said as it appealed for $21.7 million in aid.

Help is needed for emergency surgery, while safe food and water is essential to prevent diarrhea spreading among survivors living in crowded, unsanitary shelters, WHO said.

Antibiotics to treat pneumonia, another major risk, is also a priority as victims have been camping outdoors in freezing overnight temperatures.

The agency also warned about the possibility of a measles epidemic, as only 60 percent of children in the region are protected.

Health experts have also warned of potential disease threats from devastated public sanitation systems.

The U.N. refugee agency said it has begun to distribute relief and shelter items -- including plastic sheeting, mattresses and tents -- for 100,000 people.

The U.N. High Commissioner for Refugees said the agency is receiving reports that Afghan refugees are among the dead in the Mansehra district in Pakistan's North-West Frontier Province. The UNHCR said entire villages are reported flattened in the area.

The World Food Program said its first convoy of trucks with emergency food rations has arrived in Abbottabad, Pakistan, the first in what the WFP said will be multiple deliveries of high-energy food bars flown from Europe.

"We are doing all we can to get this food where it is needed most as fast as possible," said German Valdivia, WFP representative in Pakistan. "It will be enough for 400,000 people ... for the next two days, by which time we should have established a proper supply line."

Valdivia called the situation "increasingly desperate" and said many areas have no safe water, no electricity and limited food supplies.

"They are living out in the open in the mountains, and it is extremely cold," Valdivia said in a news release. "We will be providing one million people with ready-to-eat food over the next month."