U.S. President Barack Obama has marked the nation's Independence Day by welcoming 25 active duty U.S. service members as new American citizens.

Mr. Obama said in a speech at the White House Wednesday that “immigration makes America stronger” and “positions America to lead in the 21st century.” The 25 who took the oath of allegiance hailed from 17 different countries, including Mexico, Colombia, Nigeria and Russia.

Wednesday also marks the 14th birthday of Mr. Obama's daughter Malia.

Meanwhile, Americans celebrating the nation's Independence Day are facing more extreme heat, continued power outages from Friday's violent storms in the east and a threat of more fires in the country's dry west.

Tens of millions of people are lining parade routes and attending picnics, concerts and family gatherings to mark the 4th of July holiday. But with more than one million people still without power, many Americans are not in a very celebratory mood.

In a number of communities across the country, the record heat, storm aftermath and threat of wildfires have forced officials to cancel festivities, including planned fireworks displays. And many residents were being advised not to set off their own fireworks because of the risk of fire.

This year, the 4th of July marks the 236th anniversary of the country's declaration of independence from Britain.

Across the country, citizens display the American flag and proudly wear its colors of red, white and blue as a symbol of the nation's freedom.

Washington is hosting one of the biggest U.S. Independence Day celebrations, with hundreds of thousands of spectators donning their red, white and blue and packing the National Mall for a nationally-televised concert and a huge fireworks display. But a chance of showers and thunderstorms could put a damper on the celebrations.

Fireworks also will light the night skies over hallowed battlefields from the War of 1812 and America's 19th century Civil War. Similar festivities are slated for Philadelphia — the nation's first capital — Annapolis, Maryland and New York City.

Drafted by Thomas Jefferson in June 1776, the Declaration of Independence is America's most cherished symbol of freedom. The Continental Congress formally approved the document weeks later, on July 4.

Last week's band of violent storms, known as a derecho, killed at least 24 people throughout the midwestern and eastern U.S. and prompted President Obama to declare West Virginia and Ohio as federal disaster areas. Utility crews are scrambling across the region to restore power and give residents a relief from temperatures that have soared above 40 degrees (Celsius).

Residents in many parts of the western U.S. are still trying to cope with massive wildfires that have destroyed hundreds of homes and forced tens of thousands of residents to flee.