US Secretary of State John Kerry (L) and Russian Foreign Minister Sergei Lavrov shake hands at the conclusion of a joint press conference following their meeting to discuss the crisis in Syria, in Geneva, Switzerland, September 9, 2016. (AP photo)
The Syrian army says a nationwide ceasefire brokered by the United States and Russia has taken effect across the war-ravaged Arab country.
The “seven-day regime of calm” came into effect at 7 p.m. (1600 GMT) on Monday and would last until midnight Sunday (2100 GMT), the army said in a statement. 
It added that the truce would be applied across Syria, stressing that it reserves the right to respond to any violation by "armed groups."
The agreement's initial aims include allowing humanitarian access and joint Moscow-Washington attacks against militant groups, which are not covered by the agreement, including Daesh and Jabhat Fateh al-Sham, formerly known as al-Nusra Front.
The truce is the second attempt this year by Washington and Moscow to halt the war in Syria which started in March 2011.  
On Saturday, the US and Russia announced the deal in the Swiss city of Geneva after some 13 hours of marathon talks on the Syrian crisis in order to put peace process back on track.
Moscow supports the government of Syrian President Bashar al-Assad while the US sponsors militants fighting against Damascus.
Hours before the ceasefire went into effect, the Syrian president vowed that his government would take back land from "terrorists" and rebuild the country.
Over 400,000 people have been killed in the conflict in Syria, UN Special Envoy for the Arab country Staffan de Mistura estimates.